MyBB Community Forums

Basically what I am trying to do is to remove/hide reputation and warning level fields for some user groups.

You can take a look at zingaburger's template conditionals plugin. There a lot of tutorials on their forum you can apply for the postbit.

http://mybbhacks.zingaburga.com/showthread.php?tid=1464

Stuff like that may apply for your needs.