What happens when there is way too much Fluid in the transmission?

It will likely boil out of a vent or the dipstick. You really don't want to overfill the transmission or engine--it should be adjusted to the Full Line, when the engine is at normal operating temperature, idling, and in Park.

Additionally, you want to drop and clean the pan and magnet, change the filter, and refill with Mercon V ATF every 30,000 miles.