Cryptic basically has to run pretty much all designs for STO through CBS, so your idea is not a possiblilty.
I wouldn't say that. It is possible that CBS would actually like this idea. It's just not something the current concept of ship-building "considers". There might be a lot of practical limitations due to that. But has it been actually asked for?
"Hey, Cryptic, how about you pick some Nacelles and allow us to use them on all ships?"
"Hey, Cryptic, how about a few new deflector dishes with the red-blue eyes and the sovereign orange?"
Maybe this is something we should actually talk about and push. I certainly would like that! And CBS might not actually oppose to that. We can already give the Galaxy-Class a different nacelle then "canon"...