yes of course he can but remember that you will have to leave the car for more than 12 hours at his place as the fluid temperature needs to be below 40C when final testing. This takes a great deal of time as the fluid needs to cool down.
He will change it when fully hot - as this provides best drain, refill it with equal quantity and wait till it cools off for final fluid level check.
This happens with almost all transmissions that are filled by overflow method, a lot of time is wasted in waiting for cooldown to test correct level.
Good thing toyota provide a filler hole, in some transmissions (e.g. Mercedes Benz, Ford etc) - its filled from the drain hole in the sump.