Mobil 1 is Mercon V rated.
It doesn't take any more space to do a complete change out.
I have done the complete swapout myself several times.
Jack the car up
Remove the lower plastic valance.
Pull the hose off the factory cooler
put your spare piece of hose on it and put it in a 5 gallon bucket.
Run the car until it quits pumping fluid
Drop pan and change filter put the pan back on
Add six quarts SLOWLY so it doesn't bubble and belch.
start the car and add fluid until it is running clean fluid.
put the hose back on.
Drive the car and check the fluid level.
Now with all that being said if the fluid have never been changed I don't know if I would change it or not.
There is always horror stories of one that was never changed going out soon after new fluid was added.
Never had it happen to me because I always changed mine.
Mike
All you really need is a 5 gallon bucket and a couple of feet of transmission hose.