Need custom attribute for mark session contains free data consumption policy

Hi All, Which FreeRADIUS attribute I can use to mark the session contains a free data consumption policy, meaning I want to set one attribute with value for the mark session for any reason like free data or expired subscriber. and also want that attribute in accounting packet. Also want to change that attribute value with CoA. Please suggest any attribute that all NAS will supports for CoA as well. Thanks Imdad