New uniforms are optional, you'd have to keep the Raiders as the Raiders (Same Uni, same logo, etc.) If you wanted to change the name, you couldn't keep the Raiders' uniforms or logo.
Also, you can't build custom unis, you have to use the pre-made uniforms/logos they make for the relocation teams. So its either you keep them as the raiders, or take a preset uni that they force upon you if you like a team name. You have 3 sets of generic uniforms they make differently for each team. I'm guessing though, in San Antonio they may have a grey and black team, because of the Spurs.