как играт с мадами в мультеплеер дапустим рассия против украины и техники возможна ?

Well thats a very general question... What kind of mod you want to make?

Gamemode? Most of the content was made with blueprints.

Maps? You can use the SDK and make your own level with the stuff already made for the game.

Faction? Its the basic 3D modeling workflow (do high poly model and then low poly, uvs, textures and then export it). If you want to add custom animations then you will need auto rig pro for make it easier.

But for all you will need SDK, is on the epic store. Also join discord, there are people that will help you in most cases.