Yeah, the character stays green and I don't believe that the roster name changes. It has been quite a while since I tested this. In the end, I find disguise kits to be fairly useless.
For a guild infiltration build, I would just go cheap. You don't need any scrolls because there isn't much heavy stuff worth stealing, especially on production shards, 100 is plenty. That way, when you get exposed, you simply use a soulstone to move the skills to another character and delete the one that was exposed. The trick is to not expose yourself until you absolutely need to. You can even go as far as using a non thief build and just add snooping and stealing when you make the steal. You don't need stealth, hiding, and ninjitsu when you have the trust of your mark, though they aren't entirely useless. And remember, in Trammel, escape is as easy as resigning from your guild!