Make the component really large so that it can not fit on any vehicle. Then, add a scale mount that affects only that component's family and reduces the size so that it is usable. Look at the Colony Ship hull, Colony Mount, and Colony modules in the Adamant data files for an example:
Adamant Mod Data 0.15.04
You can add additional planets and stars to SectType.txt. Check out
FQM Deluxe for an example. You will need the Planet Pack of the
Image Mod to see the added planets, stars and other stellar objects.