git workflow to work with a live side project

Question

git

I'm making a website on PrestaShop . Of course you have to modify to suit your needs. The engine has a system of plugins, themes, and the beginnings of OOP for overriding base classes. But in reality, everything is not too thought out, so you still have to edit system files.

I use git for development. There is a version update problem. Let's say I finish version 1.4.6 and changed the order.php system file. Released version 1.4.7 which is distributed by zip archive. My order.php changes do not conflict with changes in 1.4.7. But the update process implies that the file is simply replaced.

I can't think of the easiest way to update the local code of the engine so that my changes are not overwritten.

There is an option in the forehead. Do a diff between the code version 1.4.6 without my changes and the new 1.4.7. Then roll this diff onto a working copy. I think it will work, but not very convenient.

Surely you can somehow adapt git but I don’t understand how yet. Maybe someone has ideas?

PS The engine code is in SVN but, again, it's not clear how this can help me.