I used the tiny block to start with (either from the collector's edition or DA) so that I would have the maximum amount of choices for the hull, so you'd think it was easy to make it say, a large hull, or whichever other hull type.
Just find the .xml file for the design in My Documents\My Games\GC2DarkAvatar\ships, and change the hull entry there to be whatever size you need.
I know that if I pick the same exact race, then I'll be able to keep it, but what if I choose another? The hull starting piece is just a block, it's universal, but when I start another race, the ship is nowhere to be found.
Just make a copy of the .shipcfg file for your design (also in the same location as above), and change the sN_ prefix to the appropriate one for the other race. You can also pick the same hull style you used when you made it when customizing your race in-game, independent of the race you use.