Basicly you use a custom race and have your own native tech tree , But  in addition to obtaining the tech you traded for or got through other ways..You also open up the other races tech tree for the item traded ect ,added too your own CUSTOM race tech tree.. The reason I say more realistic is just that . If our govenment ever get's given anything. They will continue resurch on it..Just like any other civilization would....That way youre tech tree grows as your custom race does..from game to game..over time each race would be full of surprises and differences..And BIGGER FASTER MORE POWERFUL STARBASE FORTRESSES with ORBITAL TRAVEL DRIVES. or something...