How to handle Steam Playtest app

Hello. I’ve put my game on Steam, and I’ve enabled the Steam Playtest.

Now the problem is, the Steam Playtest app has different steamID (also, i’ve seperated my backend functions for playtest and final game), and that requires some changes before packaging.
I want to make the upload pipeline less error prone, so wanted to make some automation to the upload script, so I can just run a bat file, and decide where to upload.

Now the problem is, I have a variable in my DefaultEngine.ini, that tells the game which server it should connect, like this:

[/Script/MyGame.MyGameSettings]
TargetBackend=prod

also the steam appid to this:

[OnlineSubsystemSteam]
SteamDevAppId=xyz

I want to overwrite these values only when I’m packaging for playtest app. I could go into the ini files and edit manually before each build, but that’s error prone.
Is there a way to append the ini file during package? How are others handling playtest apps?