[Cheeze]

While it can take some time to check, you can know if your retrofit orders can be carried out before you attempt it. Simply look at the cost of the new design and compare it to the construction cost of the old. If it exceeds 50%, you have two options.

(1)You can decide not to retrofit.
(2)You can create "interim designs"..which make some improvements and allow you to go step by step to your final design.

Option 2 is my general choice. Sure you have to take time figuring out how to do this (I've had retrofit plans that take 3-4 turns and designs), but it makes it more fun, as I have to weigh out not only retrofit and maintenance costs, but how well can I afford to leave ships semi-helpless while they are being redesigned into more powerful, effective ships.