URL Rewriting on Forward Proxy

You mean for example the URL www.help.com/ is asked by the client
where you want the proxy to remove ?afi_fz=cr& so the proxy will request the URL www.help.com/ei=nOa-MrJ_5Cw

If so, this is not possible - sorry.

Regards
Sebastian

Yes, that's exactly what I meant.

Thanks for the quick response

This is exactly what the UTM does with the SafeSearch Browsing or the Google Apps. But it's only possible in those defined scenarios. So, I'm pretty sure this could be configured somewhere below the GUI in the CLI. But this would void your support, and therefor it's not suggested to do so.