Updating a Customized Theme
When using the Theme Updater App to update your theme, if the app finds any custom code or modifications to the original files, it will attempt to replicate them in your new updated version. If the customizations are complex and the app is unable to carry them over fully intact, it will identify the files in question and notify you, so that you have the opportunity to update them manually.
If you are using the 'Pro-Plan' of the Theme Updater App and get notified that there are customizations that need get brought over manually after the update, you can click the 'View template file customizations' link in the popup to view the line-by-line breakdown of the code changes:
Once you click 'View template file customizations' a new page will open that lists all of the files that still require manual updates. The file names will be at the top (ex: assets/app.js.liquid) and you will notice that there will be parts of code highlighted in red and other parts of code highlighted in green:
What do the red and green colours mean?
The red areas are the code in the default version of the theme you're updating from. The green areas are the additions made from customizations. Once you change the values in the red areas to those in green, your customizations should be successfully re-added to your updated theme.
You may have to do a bit of assessment to see how to bring forward these changes in the updated theme as the lines in the files may not match up or new/updated features in the theme may have caused the code to move files. Like the code of our themes, the customized code of your theme may also need to be updated periodically, to maintain compatibility with the updated theme and to maintain your altered functionality/design requests.
We suggest keeping in touch with the developer who committed these modifications to the theme, so they can update their customizations to be compatible with the default functionality of the updated theme. Alternatively, Shopify Experts can address the update on your behalf, aware of your past customizations to be sure they are maintained as the default code of the theme changes.