Ok my town bike (v brakes)has seen better days, wonky wheels and dodgy forks and its not worth the repair. I do however have a spare set of disc wheels on xt hubs and cassette. My plan is to get a set of discs for these wheels and do a wheel change when i am using it on the road.
Does this work or will i be constantly re-aligning my calipers?

Mavic and Hope do shims that sit behind your rotors to sort out the spacing. Be prepared for lots of fiddling and wheel swapping to get it working though..

Works well. You can get some thin washers or shims to move the disk so both wheels match if you need too but I’ve swapped a couple without needing to. Still better to have a whole ‘pub bike’ for town use IMHO, though.