Accidentally. I had just changed the motor oil earlier in the day and was finishing the day by changing the ATF and filter. I had a bottle of the motor oil still sitting around. The bottles happen to be exactly the same shape except the cap on one is black and the other is gray. Of course, I had mentally noted to myself to be careful about that earlier in the day....

I haven't noticed any difference in shifting other than it being a little smoother and quieter due to the new filter and fluid (I would assume). Apparently motor oil will expand rubber seals a little but I'm hoping the amount of motor oil added was immaterial.