It is perfectly all right to ask us to change your username if you are unhappy with it.
What we do not allow is people registering with more than one name and hiding their true identity. People will do that to promote their own business, for example, or sometimes to masquerade as a person from another website.
Or sometimes they just want to distance themselves from some past posts.
Now, if you ask for a simple change in username you will still have the same posts, just under a new name. We also get requests from people to delete their accounts entirely, usually from people who were seeking cruise mates to sail with... We also honor those requests.