Since other people have answered, I'm just going to note a bit of terminology: a monk's ID is the node_id of his homenode. you have an ID of 5403, I have an id of 25047. (This raises the question, why are you asking to change your name 3.25 years later?) The term you wanted was "name". (Title is also approprate, because a user is just another type of node, but that's too easy to confuse with "rank".)

As to the actual answer to your question, it's the same as others have said: ask one of the gods (IE /msg gods Can you change my name to foo?). They're likely to say yes iff:

• Your new name isn't already taken.
  AND
• You don't have a significant reputation associated by users with your name. (That is, actual human reputation, not XP.)
  OR
• Your new name is recognizable by humans as the same person as the old one.