Hello
TOO
I've got quite a bit of recent experience fitting ADSB capable transponders to light aircraft and in your case would point you to this unit..
https://www.trig-avionics.com/product/stack-transponder/
Not found changing codes fiddly at all.
It is a virtually plug-in replacement for the KT76 and is ADSB out with the correct GPS feed or one of these..
https://www.trig-avionics.com/produc...-gps-receiver/