Ok this is my problem i want to add new units to the Custom Republic side but what do i need to do ? DO i need to create a Mission.lvl ? If so how do i do that

If you're trying to add units to a custom side, then you edit that custom side. Mission.lvl only holds the map and video config scripts for the official maps. I don't think it has any side resources in it.

Aww I meanth for the Default Republic's side