You can already change talkgroups using your radio. Please see the user manual:
http://manuals.sharkrf.com/openspot2/en/nxdnreflector-connector.html#page-top
http://manuals.sharkrf.com/openspot2/en/p25reflector-connector.html#page-top
"You can switch NXDNReflector/P25Reflector servers with your radio by calling the desired server's ID with a private call."