Welcome to the forums. I'm sure you can pull a lot more than 800 lbs without damaging anything. My guess is that the tow weight is rated low because of the lightness of the ATV. Even though you can pull a lot more than 800 lbs, it will be harder to safely stop more than 800 lbs. I would tow in ESP mode, though.
Most 4-wheeler problems are caused by a loose nut connecting the handlebars and the seat!!
You only need two tools in life -- WD-40 and duct tape. If it doesn't move and should, use the WD-40. If it shouldn't move and does, use the duct tape.