I stopped before I changed his wardrobe since I worried about screwing the whole neighborhood and quit without saving.
I've found Christianlov's clothing rack at MTS2 to be the most reliable way to change an NPCs clothing. The NPC will come onto the lot, change into the outfit you select and then leave. Other methods often leave the NPC behaving strangely or not keep the newly assigned outfit.
I think it also allows for plastic surgery and hair change, but it's possible I'm thinking of one of his other tools. Although I haven't specifically tried these on the butler yet, it has worked for other NPCs I've altered.