So it said that your old username will forever be on record. So, can someone take that username since you're not using it now? If you wanted to, could you change you username back to what it used to be?

Once you change your username the old one is free for use. That means any user could make an account with that name, or change their account name to it. If you change your mind you can change back to the old username for the same fee, provided it is not taken already.

Yup, if you change your name, someone else can take it. You can change your user name back to what it was, if no one else has taken it in the meantime.

Thank you both very much :)