For any modifications in UltimatePOS, we recommend the below approaches to help with easy modifications:
If you want to do a lot of modifications we recommend that you create it as a separate module.
Use Custom view files to make any modifications in view files.
Use separate files for all adding custom js/css/php code.
If none of the above approaches works, then we recommend that you update UltimatePOS to the latest version & merge your changes into latest codebase.
