I don't find any information on being able to change the look of your NPC Adventuring Fellow other than tossing your pearl to the ground and starting all over from the beginning. This really isn't a great option for people who have high level NPCs.

When they were first released, you could only choose the top three models for each race based on the Vana'diel Census. Later, it was expanded to include all models of all races (If I'm understanding properly.). I've since fallen for another face model preference which wasn't in the original three, and I wanted to change it.

There should be an option somewhere to change your NPC's model. While I don't personally see a problem with changing your NPC's race, I can't find any form of story reason that it could happen. Maybe if you went with Fellowship Points. Same for their name.

What I CAN think of is a way to change your NPC's model that could fit in a sensical manner. While Fellowship Points could be used here, I think that a mini-quest could go on talking to your NPC at the Rendezvous Point and suggesting like "Ever try a different look?" You then get the chance to do something to choose your NPC's new look, either by re-doing the original quest that designed your NPC, or just telling your NPC how to look.

I just want to change my level 66 NPC's look since I'm kind of unhappy with my choice now, but I don't want to redo all the quests and leveling again. =(