If you are just adding the oil cooler then really you just need to account for lost fluid plus the capacity of the cooler and lines.
My view is that you only need to go through that procedure if you are doing a fluid replacement. I had Infamous do the procedure when they installed my SSP valve body. They warmed the car to the set temperature but I don't think they kept the car running immediately after. If you do, the temperature will exceed the target range. If you take too long on the drain and overfill then you might need to restart the car to hit the target again. They did it all on a lift which is much easier.
If you want to just top off the "right" way - I think you would add a quart, warm up the ATF to the right temp (shifting slowly from P to D and back), turn off the car, open the drain and wait for the fluid drain to be a hair-thin. That's what I understood anyways. The car needs to be level when draining.
Sithspawn has way more knowledge then me and should verify though
