Can you explain what exactly you want to do?
A friend asked me to think about an additional repeater at OE3XNK on 23 cm. I did some research on the net how to use SDR for that purpose and found QRadioLink. Have not tested it so far as it seems to be quite complicated for setup. There is also one information on the net how to use a simple script within the Pluto itself to copy a signal from RX to TX. For me GNU-Radio possibly seems to be the best solution.
It should be at least a standard FM Repeater within the 23 cm band. But I think it this works the frequency could be changed easily to other bands or to crossband. I think there will be no need to decode the FM on RX and modulate on TX. Therefore maybe a linear repeater would be best.