You just create functions for what functionality you want to represent.
Anything that you want to run on a Class-World’s Startup must be executed on BeginPlay, the exception being construct script (sets default values).
If it’s variables that you want to set, you could simply set them to a specific value if you know where you’ll be. For example, even though you could have one Character Class and IF break everything, you could Create a Base Character Class with minimal required info, then create two sub classes. If you know your world will start with App A, then run Character_A.