Oh, you are the one that made that other post. Yeah, you have to make it a mutator instead. Look up how other mutators are made. Basically, you make a main file that changes things in-game actively as the game runs it's vanilla ways. Using checkreplacement, you can change infantry with a custom infantry (usually an existing infantry in model and all but with changed damage or range or health), or a vehicle with a custom vehicle, or the purchase system which itself is an actor just like a vehicle or infantry. After you get the game to switch at game-start "Purchase_System" with "Purchase_System_Modified", you can make purchase system modified your "modified purchase system file", and make your additions in there.
For instance, look up pre-4.03 balance mutator, and stank mutator, as they are similar and you can download then and understand what they did. Stank Mutator actually changes the Purchase System, you can start with it, and switch the changed purchase system with your own purchase system (and rename what you need as necessary).
You have to pack it with UnrealFrontend so consider giving the RenX SDK a download.
Thanks, never worked with UE before and tried the minimal with the mutator and didn't seem to work so I tried it the other way. Going to take a look at it!