Override DefaultEngine.ini values when packaging

Hello
I’m wondering if it’s possible to override some of the .ini files, when packaging a project.
I’m using RunUAT.bat to build and package my game for uploading to steam, however I have a Steam Playtest enabled, which requires different AppId.
I want to avoid human error, so I’m making a batch script that builds and uploads my game.

For this I’d like to overwrite some values in the DefaultEngine.ini (SteamDevAppId, and some custom made ones) just for the package, without actually modifying the file, since I want to be able to build both for Playtest, and for my main app.

Is there any way to do it? Either append an ini file (like making a PlaytestEngine.ini file, that only contains the overridden values), or directly overwrite the values somehow?

How do others handle playtests, and different config values for different builds?

Thank you!