I can't see any reason to transfer water from one tank to the other. I do major water changes on my Mbuna tank weekly and sometimes up to 90-95% without any stress problems. In fact they actually seem to enjoy it once the tank is filled back up. Don't forget to use a water conditioner.
I would remove all the decor from the old tank and place any that you would like to keep in the new tank. Next, I would transfer the filters or the bio material from the old tank to the new. Drain the old tank untill it would be easy to catch your Severums and use a net to quickly transfer them to thier new home. Their a lot hardier then you might think.
I would remove all the decor from the old tank and place any that you would like to keep in the new tank. Next, I would transfer the filters or the bio material from the old tank to the new. Drain the old tank untill it would be easy to catch your Severums and use a net to quickly transfer them to thier new home. Their a lot hardier then you might think.