As a simple expedient , for some quick pcb fabs I combine a few designs and then cut the boards when they arrive . I don’t bother with v cuts
To do this in Kicad , I’ve just cut and pasted the two designs from pcbnew into a third blank pcbnew instance. That all works fine.
I do note no net information comes across , so I can’t allow things like board fills to ever update as it disconnects everything.
Is there a way to do this and preserve the net information.?