Well, the original Strategic Operations (CGL, 2nd Printing, 2011) did say this on p. 189: "DropShips, JumpShips, WarShips and Space Stations can only be customized with the assistance of a functioning shipyard."
Now, the question is: how hard is it? In my head it is not very, given how things are routinely changed, modified, improved, or retrofitted in the BTU. And my mercenary outfit is going to keep operating like they have been for the last 25 years (not continuously, since I rarely play anymore, but...). But I'd be interested in knowing where to look for the official answer.