Unfortunately, there's no other way. If you do a lot of modification, you should use Child theme:
https://www.gavick.com/documentation/wo ... ld-themes/and of course for the css moidification you can use css/override.css file and for your own function, use gavern/user.funcitons.php file, if you want to do more modifications, use Child Theme and then you can just change parent theme folder. (every files)