[Eisenhans]

Why not solve the problem with the engines in the colony ships by giving the engines new roman numericals like that: ion engines 1 to 3, contra terrene engines 4 to 6, jacketed photon 7 to 9 and quantum 10 to 12.
The numericals can go up to twenty anyway.
It might not look nice to have a new designed kind of engine start with a high roman numerical (like contra terren engine IV for the first design of that type) but it should save the problem. Maybe some other problems could be solved like that as well.