Ummm.. No... That's not exactly how it works.. ;)
800 TW is 800 TW. What a WD hitch does is distribute that 800 pounds between the trucks front axle and the trailer axles as well as leaving some on the rear axle.
Think of a wheelbarrow. Toss a 80# bag of cement in it and what happens when you lift up on the handles? You distribute some of that weight to the front wheel, some thru your arms to your legs and some might still be on the rear skids if you don't lift it all the way up.
The 80# bag of cement has not changed.. It's still 80#.
Good luck!
Mitch