Automatically Assigning Users to Groups at Registration

[Aaron Karp]

I have a client who offers fundraising programs to schools and other organizations. I'd like to set up a system whereby the client can create a new group whenever a new fundraising effort starts. That part is easy. The tricky part is this - I want to associate a code with each group so that any user who inputs the code at registration is automatically added to the corresponding group. I saw a post about doing this using MySQL triggers, but that would mean the groups and codes have to be hardcoded. Is there a module that does this or something similar? I'm hesitant to start digging into the backend myself...