Adding ship design types

Initially when I installed, I made sure to add all my favorite ship types, like:

FF
FFG (missile frigate)
DD
DDG
CL
CR
CA
DN
BB
Repair Tender
Replenishment

I realized after playing a while and trying to build them, I forgot a couple, SC and Satellite Layer. Now when I add them into the main file under \Data, they do not show up in my empire list! And why the heck can I not add new types while playing, like in SE IV?

How do you add new types to your ship designs while playing a game? And why do updates to the data file not show up in the game?