http://wiki.mikrotik.com/wiki/Manual:RA ... ric_Values
MIKROTIK_ADDRESS_LIST 14988 19
Send back that attribute, and the user will be added to an address list on 192.168.1.3. Then you can add DSCP/TOS marks to those packets in the firewall mangle facility of that router, and have the router at 192.168.1.1 do its policy based on the DSCP/TOS marks rather than based on an address list.
You cannot add the IP to an address list on 192.168.1.1 via RADIUS because that router isn't involved in the RADIUS transaction. You may be able to run scripts on the RADIUS server that fire and make calls to 192.168.1.1 via the API and make changes, and FreeRADIUS is certainly flexible enough to do that, but that's a heck of a lot more work and potentially more fragile. I'd prefer the method I posted. But, again, FreeRADIUS does have postauthentication hooks that let you call scripts after the RADIUS traffic is done, and the API is fully documented and has libraries in many different languages - if you want to go that way.
Specific answers require specific questions. When in doubt, post the output of "/ip address print detail", "/ip route print detail", "/interface print detail", "/ip firewall export", and an accurate network diagram.