Im trying to make my first plugin but i dont understand something

Hey guys, one day I saw this github page and i tried to copy every change to my engine source code (I use the master source code). but my problem is that every time i have updates it delete my changes or ask me to submit it. So i think to make HBAO plugin as my first plugin, but when i saw the HBAO modification i saw it override some classes inside the source code (like the RHI class).
Can i make a plugin that override classes like RHI or SceneView class?

A plugin can nos change the engine source, a plugin can extend it though. The repo you are pointing to is not a plugin, it’s a complete engine fork. It makes no sense to let a plugin modify engine source, think of the pre-build version of the engine from the launcher, there you would not be able to ‘modify’ any engine source because it’s already build. You plugin can provide extended classes that you can then use in your project though, not the same as overriding.

can i extend a class (like RHI) and make my game use the extended class from the plugin?

First first guess would be no, you would have to dive deeper in the engine how those classes are instanced.