@ZIV No, you can not change your profile/member name as it causes too many problems from frequent changes (or someone hoping to get a "clean" slate). Some forums only allow it once per year (and then often charging money such as Arachnoboards), or do not allow it at all. Here though, in order for it be changed you have to put in a request with the root admin via a private message and it is his option to do the change or not.
Yes, member ranks change as you post more on the forum. The first is at 10 posts, followed by 50, 100, 500, 1000, etc. (or something like that). After the ootheca rank you will rank up through the nymph instars, then it changes to mantid species names. Each rank takes much more posts for the change though, and can be years once you hit the 1000 post mark to see any change.