Can you add a ship when....
 

There is a total conversion?
lke Borg incursion 2 or Fleet Operations?
I want to add p81 sovereign and Intrepid, but I don't want to reinstall and do all these kinds of stuff. I modifyed a lot of stuff in A2 BI2... Can you add a ship above a total conversion?

?????

Provided the game actually starts - it is always possible to add a new ship/ station whatever. The procedure is exactly the same as if the game was freshly installed. (Assuming the basic shipyards haven't been done away with.)