I’m planning on doing this one of these weekends this fall.

I think I know the answer to this, but want to see what others think.

I added an auxiliary trans cooler to mine. So the tubing currently goes:
-Trans to top inlet on radiator
-Bottom outlet of radiator to one side of the trans cooler
- other side of the trans cooler back to the return line that normally would be hooked up to the bottom outlet on the radiator.

So, what I’m thinking is that I will have to disconnect in two spots; the top inlet of the radiator for the old fluid, and then the tube that used to be on the bottom outlet of the radiator. This way I’ll basically be bypassing the internal trans cooler that’s in the radiator and my aux trans cooler.

The reason I think I’ll have to do this, is in the way the OP did it, you’re relying on gravity to refill the trans on the return line.
On my setup, that return line will be leading to the aux trans cooler, which is a decent amount more tubing and mounted in the middle of the radiator, so gravity will be working against me to get that new fluid into the aux trans cooler and through, and back to the actual trans. I’m thinking the best bet will be to just bypass the radiator and trans cooler altogether and disconnect in two spots.

Am I overthinking this, or what do others think?