as long as your declorineating your water and have a large canister with a lot of biomax than youll be better off! Breeders do daily 90-100% water changes, bc the cleaner the water the healthier the fish. aslong as you don't kill your nitrifying bacteria than you'll be good
yes a 50% water change should be safe as long as the water you put back into the tank is the correct temperature. The water itself doesnt contain too much beneficial bacteria, so you can safely perform large water changes without having to worry. Some discus keepers do water changes (sometimes with automatic water change systems but it doesnt matter) that are equivelant to 100% water changes daily.
i do 80% water changes every week on all my tanks,have been for years and never had any ill effects.
As everyone stated as long as the new water is conditioned(temp,dechlorinated etc)then you wont have any problems