is it possible to use different ship in the single player mode, other than the galaxy and soverign class?
Yes. You can use what you want, but if you can`t do it yourself, then you can use already done: Intrepid, Warbird, or Sovereign from the beggining. I recommend Intrepid - it rocks in sp, too bad there`s still no bridge for Intrepid. Download them from BCfiles.com