You won't need a rename token to use it again (as long as you don't set it up so that your old username redirects to your new username, of course). In fact, I just grabbed my former username for free. So if you really want your old username back (say, to start a new blog or community on a different topic besides the ones you address under your current username, or to focus solely on that topic as opposed to the more general mess that say, my DW is) you can a) pick a new username and pay for the rename token on it as I did, which will transfer all your current posts over to it then b) take your old username back to use for whatever you want. I think this is really neat. (With the caveat that if one of the many other MMs in the world had already grabbed my old username then this scheme would not work).