I made it work in the Game.ini file.
Just had to put the following at the start:
[/Script/ShooterGame.ShooterGameMode]
So, as an example, your Game.ini should look like this:
[/Script/ShooterGame.ShooterGameMode]
PlayerDefaultNoDiscoveriesMaxLevelUps=99
bClampHomeServerXP=false
ClampHomeServerXPLevel=99