The reason I want to change the name is very simple: I don't play poker anymore.
The name I have chosen I prefer not to say in public to avoid that someone could create an account with that same name, but it does more justice to what I currently write on the forum. I have checked that there is no one with an account with that name at present.
I support your name change request, but unfortunately it's not like a merit source application, whether the thread gets support or not, theymos does what he likes with respect to name change as there's no specific rules guiding it.
I bolded a part of your statement. The reason you chose Poker Player was because you played poker in the past and you no longer play it now. The new username you said best describes what you do now, how about in few years time, you no longer do what you do now, will you want theymos to change your username again?
I will advice you choose a username based on your personality and not what you do contemporarily.