A reincarnation token allows you to recreate your character through the creation menu while keeping your stats, skills, and mastery exp.
Note:  Mastery EXP can be kept on previous race or transferred with a bit kept on the previous race. This is shown visually in the creation menu!

You'll be able to change the following:
Your Race
Your Class
Your Character Name
Your Character (Face, Body, and other Creation Options)

/character reincarnate
while having one of these tokens will allow you to recreate your character