Problem with attribute transfer to an external script

Hello. We use FreeRADIUS as an intermediate server (proxy) between commercial billing system and radius clients (NAS, servers, etc). In this case it is a question about SIPProxy. The billing system sends some additional attributes. Here a example from FreeRADIUS log: rad_recv: Access-Reject packet

How it is better to start a script in FreeRadius to change User-Name and realm at proxing?

FreeRadius is used for proxing ([EMAIL PROTECTED]) to others RADIUS servers. Also we change the some attributes at proxing. Некоторое время назад была задача при получении accounting менять аттрибут User-Name в зависимости от аттрибутов User-Name, Calling-Station-ID, Called-Station-ID, ... Some