I dunno. I was able to load up Cubby's game, add a test league with fictional players, delete it again, delete all free agents to eliminate scrubs, edited MLB to add two brand new teams, released all players and scheduled inaugural draft, took control of the expansion Denver Sand Gnats, maneuvered the draft order so that the Gnats were first, found Barry Bonds, took him with my #1 draft pick, and made him a Sand Gnat as his just reward.
Cubby's roster is just another saved game with tailored rosters, logos, uniforms, and such. It should operate like any other saved game. Note that in order to do what I did above, it was preseason (which it is when you first call up Cubby v. 3.0 at least) and I was commissioner in order to maximize my creative powers.