upgrading 3.0.3.8 to 3.0.4.0 without Themes?

I would like to upgrade from 3.0.3.8 to 3.0.4.0 I have done custom work on the default theme twig files (edited through ftp)
To do an upgrade do I need to overwrite all of the default theme twigs? I have also changed the default name of the admin, will that cause an issue or should I rename back to admin before I start. What I understand is that I need to upload all the files except for the config files, then go to http://<yourstore.com>/install and install. As long as my extensions are compatible with 3.0.4.0 then everything should work??? Should I make the change to php 8.2 before or after the upgrade?