2.Change price.
3.Sell some more products.
4.Send lawyers to collect diff on product sold in [1].
The question is, was he made aware, that his previous agreement will be changed when he was giving some more money?
Any new pledge could easily have a little tickbox "I've read and understood the terms & conditions", I'm not sure if Kickstarter has one but I've seen such boxes pop up everywhere.
We also need those contracts to be much simpler. A single page of large font in language simple enough for a grade school graduate to understand what's supposed to happen.
Yes, a few rights are better protected then in the US (at least if you haven't written the EULA in the right way), but I'm pretty sure they are generally legal and enforced.