Lastly, a refit kit that includes an engine drops the class for engine work from E to D.
So the answer to your question comes down to how much credit you want to give the Capellans. Personally, I'd say they developed a Refit Kit to speed up the conversions.
The engine change would normally mean a Class E refit, requiring a factory (Campaign Operations, page 212). But the Refit Kit section on that same page specifically says:Class D refits can be done at a Maintenance Facility instead of a Factory.So the answer to your question comes down to how much credit you want to give the Capellans. Personally, I'd say they developed a Refit Kit to speed up the conversions.
Changing engine type and/or rating (unless done via a refit kit; see below).