I’m linking the official method video below. It’s a drain and refill. Temperature of the CVT fluid/pan has to be checked (3 methods to check temp) to make sure you do not underfill or overfill the transmission, specially when the oil you drain is already hot and the one you pour in is at a different temperature / colder. He’s doing it for Camry but same method is for sealed Toyota CVTs.
We also have a thread for it here at pakwheels if you want more details . Do same Drain/refill like 3 times to have most of the oil replaced.
Now coming to your point about opening the pan.
Look if it’s done by a skilled person, all gaskets properly taken care of / replaced with new, AND fluid temperature level is adjusted at the end to make sure it is not over or under filled, then that too is fine but a much bigger risk if someone is not following the correct procedure.
And lastly
Our people worry too much about changing CVTF frequently. Toyota says for normal driving conditions CVT fluid is for lifetime no need to change (many Toyota dealerships won’t change CVT oil at all in the US), but it’s still a good idea to have it replaced roughly 60k miles or 100k kms if driven in extreme conditions like towing or mountain driving or extreme stop and go traffic.
