Radius Proxy for Authorization

Hi, I am very new to radius and need help to confirm the following. I have an existing radius server running on Cisco ACS 4.2. In the current configuration, all users are configured using priv ID 15. I wanted to setup a proxy radius, where the proxy will relay an authentication and authorization request to the Cisco ACS, but when relaying back the authentication and authorization message back to the clients, I want to overwrite the priv ID with something other than 15 (for eg, user XXX -> priv 14, user YYY -> priv10, etc). Is there a way for me to do that? Or is this behavior is actually prohibited by the standards? Thanks in advance, LMR