Customising a Shopify theme is where a lot of stores quietly paint themselves into a corner. A well-intentioned code change, made once to achieve a specific look, ends up blocking every future theme update because the developer's next release would overwrite the very files that were edited. The store ends up frozen on an old theme version, missing fixes and new features, purely because nobody wanted to risk losing the customisation. There is a better order of operations, and this guide walks through it.
Why customising a Shopify theme breaks updates
A theme update from its developer replaces the theme's underlying files with new versions. If a store owner or developer has directly edited those same files to add a customisation, the update either overwrites the customisation entirely or, if applied more carefully, creates a conflict that has to be manually resolved file by file. Neither outcome is pleasant, which is exactly why so many customised stores simply stop updating their theme altogether, quietly accumulating risk as the theme falls further behind the platform's current standards.
The safe layer: settings, sections and blocks
Modern Shopify themes, built on the Online Store 2.0 architecture, expose a wide range of customisation through the theme editor itself: colours, fonts, section layouts, and the ability to add, remove and reorder blocks within a page, all without touching a line of code. This layer of customisation is stored separately from the theme's core files, so a theme update generally does not touch it at all. Working within this layer first, before considering any code change, resolves a surprising amount of what store owners assume needs custom development.
App blocks instead of pasted code snippets
Where a store needs functionality beyond what the theme's own settings offer, an app that provides its feature as an app block can be placed directly into a section through the theme editor, in the same way a native block would be. This is a meaningfully safer path than the older practice of pasting a snippet of code directly into theme files, since the app block lives outside the theme's own code and is not at risk when the theme updates. When evaluating an app for a specific feature, checking whether it offers a proper app block, rather than requiring a manual code snippet, is worth doing before installing it.
When code edits are genuinely unavoidable
Some customisations do still require editing theme code directly: a layout the theme's sections cannot achieve, a specific interaction no app covers, or deep integration with another system. When this is the case, the goal shifts from avoiding code edits entirely to making them in a way that survives future updates as gracefully as possible, which the remaining steps below cover.
Working on a duplicate theme, always
Shopify allows a theme to be duplicated within the admin, and any code-level customisation should happen on that duplicate, previewed thoroughly, and only published once confirmed working correctly. Never edit the live theme's code directly. This single habit is what turns customising a Shopify theme from a live-site risk into a safely testable change, and it costs nothing beyond a few extra clicks to set up.
Keeping a change log
Every code-level customisation deserves a short written record: what was changed, in which file, why, and on what date. Without this, a future update that conflicts with the customisation becomes a guessing game about what the original change was even for. With it, reapplying or adapting the customisation after an update becomes a straightforward, documented task rather than an investigation. This matters even more when the person applying a future update is not the same person who made the original customisation.
Updating a theme that already has code customisations
When an update becomes available for an already-customised theme, apply it to a duplicate first, then compare the updated files against your customised ones, reapplying each documented change individually rather than overwriting everything blindly in either direction. This is more work than a single click, but it is exactly the work a change log makes manageable, and it is far less work than rebuilding a customisation from memory after an update has already overwritten it.
Version control for anyone comfortable with it
For stores with a developer comfortable using it, keeping customised theme code in a version control system alongside Shopify's own theme editor gives an additional, more precise record of exactly what changed and when, beyond a written change log alone. This is not necessary for every store, particularly smaller ones with occasional, simple customisations, but for a store with frequent code-level changes it adds a layer of safety that a plain text log cannot fully replace, since it captures the exact change itself, not just a description of it.
When to rebuild rather than keep patching
If a theme has accumulated years of undocumented code changes, and updates have been skipped for a long time as a result, there comes a point where cleanly rebuilding the customisations on a current version of the theme, or on a different theme entirely, is more efficient than continuing to reconcile an ever-growing gap. This is a judgement call based on how many customisations exist and how well documented they are, but it is worth recognising as a legitimate option rather than assuming the only choices are "keep patching forever" or "never update again".
What to brief a developer with
When bringing in outside help for a code-level change, a clear brief speeds things up considerably: describe the desired outcome, share the existing change log so the developer understands what has already been customised, and specify whether the change should go on the current theme or a fresh duplicate. A developer working from a well-documented starting point can usually estimate and deliver a change more accurately and more quickly than one starting from an undocumented theme with unknown history, which also tends to keep the cost of ad hoc customisation work more predictable over time.
Reviewing customisations periodically
Even a well-documented set of customisations benefits from an occasional review, perhaps once or twice a year, to check whether anything can be retired now that a theme update or a newly available app has made a piece of custom code unnecessary. Customisations tend to accumulate without anyone revisiting old ones, and a store that periodically asks whether each documented change is still needed, rather than only adding new ones, keeps its customisation footprint leaner and easier to manage over the years.
Handling third-party integrations during customisation
A store's theme rarely operates in isolation; it often needs to work alongside integrations such as a loyalty programme, a subscription tool or a custom checkout extension, each of which may have its own compatibility requirements with theme code. Before customising a Shopify theme in a way that touches areas these integrations rely on, checking their documentation for known conflicts saves discovering the problem the hard way, after a change has already gone live and something else on the store has quietly stopped working as expected.
Testing across devices before publishing
Any customisation, whether achieved through settings or code, deserves testing across a genuine range of devices before going live, not just a desktop browser at a comfortable window size. Mobile shoppers make up the majority of traffic for most stores, and a customisation that looks perfect on a wide desktop screen can behave unexpectedly on a narrow phone screen if it was never actually checked there. Shopify's theme preview tools make this reasonably quick to do, and skipping it is one of the more avoidable ways a well-intentioned change ends up causing a real problem for the majority of visitors.
A practical checklist before any theme customisation
Before making any change, work through these in order: can the theme's own settings achieve this, can an app with a proper app block achieve this, and only if both are genuinely no, proceed to a code-level change on a duplicate theme with a documented record. Following this order consistently is what keeps a store both distinctive and upgradeable, rather than forcing a choice between the two.
Signs a store's customisation approach needs fixing
A few patterns suggest the current approach to customising a Shopify theme has drifted into risky territory: nobody remembers what a specific piece of custom code does, the theme has not been updated in a long time out of fear of breaking something, or every small change requires a developer because the store's structure has become too fragile to touch confidently. Addressing this before it worsens, ideally by documenting existing customisations retroactively, is worth prioritising even if no new changes are planned in the near term.
Balancing distinctiveness against upgradeability
There is a genuine tension between wanting a store to look and feel distinctive and wanting it to stay easily upgradeable, and it is worth naming honestly rather than pretending it does not exist. A store that leans heavily on custom code to achieve a very specific look accepts more of the maintenance burden described above in exchange for that distinctiveness. A store that stays almost entirely within the settings, sections and app block layer trades some visual uniqueness for an easier, cheaper long-term maintenance path.
Neither choice is wrong; the point is making it deliberately, for each customisation, rather than drifting into heavy code reliance without weighing the trade-off. Our guide to free theme vs paid theme vs custom build covers a related version of this same trade-off at the point of choosing a theme in the first place.
A quick reference for common requests
A few requests come up often enough to be worth naming directly: changing a section's spacing or colours almost always belongs in the theme editor's settings, not code. Adding a genuinely new layout not offered by any existing section usually needs either an app block or, if nothing suitable exists, a documented custom section built specifically for that purpose. Changing how the cart or checkout behaves deserves particular caution, since these areas are more sensitive to conflicts with apps and Shopify's own updates than most other parts of a theme, and are worth testing especially thoroughly on a duplicate before publishing any change to them.
What this means for a store's total cost over time
Approached with this discipline, customising a Shopify theme stops being a source of recurring, unpredictable cost every time the theme updates, and becomes a one-time investment that keeps paying off. Stores that skip the change log and duplicate-theme habits described above often end up paying a developer repeatedly to untangle the same conflicts every time an update is needed, a cost that a small amount of upfront discipline would have avoided entirely across the life of the store.
Getting Shopify customisation right from the start
A store built with this layered approach from day one, settings first, app blocks second, documented code changes only when genuinely necessary, stays both distinctive and easy to keep current for years. Our Shopify store development service builds and maintains stores with exactly this discipline. If your store has drifted away from this and updates feel risky, get in touch and we can help bring it back under control.