Probably going to need to underexpose even more. LED displays are typically quite bright, so it's likely that if you can't dim them down temporarily for the shoot you're going to have to underexpose to the point you can't see anything else around...
Nope, they used serial for the external connection at that time
https://mavicpilots.com/threads/here-are-the-pinouts-of-the-mavic-pro-battery.117094/
And you need access to the inside anyway to recharge the battery a bit since the BMS...
No, you'd have video playing at half speed.
But if you do nothing and work on/export a 4K30 timeline your video editor will drop half the frames on its own.
All that's left is a faster shutter speed but unless your subject is very specific such...
Well if your fingers slip while it's fighting you flipping it you'll have a nasty surprise... but no it won't care about spinning the motors faster, that's what it does all the time in flight anyway.
What did you expect? DJI's not going to tell people to do "potentially more dangerous than they need to be" things.
Flipping it works but is even more dangerous than just a normal hand catch and stop motors, but... you do you.