[Serusers] Help rewriting "To" URI

Hello, I've been working whit SER for a while, and I need to have some way of redirecting Invites dynamicly. The idea is similar to the definition of groups (local,ld,...), only I want to be able to define the redirection address without having to rewrite ser.cfg (and therefor reinitialize SER). The part of defining these new groups and addresses was straightforward, after that I tried to build a module that would have a function to do the writing of the "To" URI. The only function I found to alter the destination URI was append_branch. The module compiles without error and SER works normally, except it does not do the redirections that I was hoping. Are there any other ways of adding/rewriting something to the body of "To" in the SIP message? Or one can only do that in ser.cfg? Thanks in advance, José Nunes