EOS packaging modifies the config stored in the engine, but if you installed UE5 with epic games launcher, it won’t allow you to modify the engine. You need to download the engine source on github (Downloading Unreal Engine Source Code | Unreal Engine 5.0 Documentation), then run the downloaded Setup.bat. Once that is done, you can follow instructions here: Using Epic Online Services with Lyra Starter Game | Tutorial
So you won’t need to modify the engine code yourself, but you’ll need to use the github engine version to have a “custom” engine for your project.