'Nay, just make for example APB II to do the same damage as APB I but shrink by say, 5kt."
This is a pain.
Why? When retrofitting ships, they must be the *exact same tonnage*. So if you just press the upgrade button and leave it at that- or end up with space left over you can't use because of the shrinkage- you won't be able to retrofit to the new design.
Phoenix-D