I think you have a CD4E transmission, which had a drain plug. You can remove it and get about 3-4 quarts out. Refill with any Merc V equivalent. If it were mine I'd give it a try.
Where exactly is this plug? I need to do the fluid in my girlfriends car. I'm also going to use a pump in the filler tube to get more out. Also, did the 1999-2000 Mystiques come WITH Mercon V from the factory? I know they said to switch from Mercon to Mercon V in a Ford bulletin and I'd rather not mix them if I can help it.