An individual would risk corporate lawyers lobbing suits at them they don't have nearly enough resources to fight. In that way, it's much like other forms of activism: individual actions are easily singled out and retaliated against.

If a ton of people were to do so, however, they might have an impact. Either the registrar would have to take steps to limit who can submit them, which might conflict with some laws, or they'd invest a great deal of resources trying to sort out the legit ones. Trying to single out people for retaliation is hard when there's enough of them. In this way, too, it is like other forms of activism:

There is strength in numbers. There is power in unity.

If, hypothetically, someone were to coordinate such actions in the style of a crowdsources DDoS, and they could get enough participants, they might get away with it.

Getting sued for all your bananas by companies much richer than you.