I just swapped out my upper corner marker bulbs to 194 LED bulbs an hour ago.
The 10mm was a bit loose, so I used a 9mm open end wrench and that fitted perfectly.
The problem was that the 9mm wrench wasn't long enough. So, I used a piece of half-inch conduit tubing and pressed it over the 9mm wrench and it worked great.
I used a short piece of metal coat hangar and curved the end of it and used that to snag the fixture and wires to pull it out to change the bulbs.
Zip, zip, zip... and done in 5 minutes...