Undid the wrong bolt for trans fluid (bottom bolt)... issues
 

Man, what a day. I was sick just starting to get better (but far from 100%) so I went to the track. I decided to do a fluid swap for some reason, idk why. I had 90 min to kill so why not.

First, I drained using the bolt underneath the transmission, not the side. It has a torx/star pattern. I didn't notice anything strange or any springs pop out or anything, but I can't figure out if I screwed up anything (Miatas, for example, definitely have "do not open" bolts)

Then I put the Miata MTF in there. Doh! Saw that after 2 sessions. Drain and refill. Looked really thin and almost gray- like muddy water kinda. I'm not worried about the wrong fluid causing damage (it was MTL, so it's fine), but the color on it was disturbing for 45 min of driving. Made me concerned I screwed something up with that bolt and metal was shearing into the oil or something.

But it felt fine.

I did exactly the same thing last year.
https://www.ft86club.com/forums/showthread.php?t=153051

There is a ball that goes in there but as far as I can tell the little torx bolt is used for assembly only. I have since noticed that 2nd gear can be quite notchy when cold but is perfect when warmed up.

Regarding used the complete wrong fluid in there, I doubt that it would cause any major issues.