Correct me if im wrong but, depends on the size of you tank IMO. If your tank is 1.5 gallon or below then I would say no. Then I would reccomend you remove the fish and re acclimate him. But, for 2 gallon and up you would always be leaving at least a gallon of water in the tank.
I always remove my fish and re acclimate them. But, you don't have to if your really really careful.
If you do leave them in for 50% water changes I would reccomend you get some airline tubing and get a siphon going to put the water back in. That way, the water goes in slowly and you don't have to stand there for 10 minuets pouring water into a your tank.