There's going to be a new update coming soon where you can change your usernames! :D
You can also use some already used usernames if they don't have a certain amount of cheese to be protected.
I'm not sure what the amount of cheese/whatever stat you'll need for your username to be protected but you could start looking on cheese.formice.com for usernames you want for your account/your alt account if you don't like it by simply typing in cheese.formice.com/mouse/USERNAME or just searching it on http://www.cheese.formice.com/search , the first option goes faster though.
Share your opinion on this update on this thread~
I just worry about new people joining and having their usernames taken and then not being able to log in because someone took their username before they met the certain amount of cheese/whatever needed for their username to be protected xP