I was just about going to mention this as well, it's what we call the 'potestatieve voorwaarde' in dutch law, and it it causes a lot of legal issues (let's say it's forbidden in 99% of the cases). This wouldn't have been the case if you had been more specifically about the circumstances under which the contract could change. Of course, there's probably hundred of other remix competitions with the same foggy and dodgy rules, but that doesn't make it any more legitimate...
I'd say article 9 should be read together with article 11, which has a way more concrete basis. Article 11 mentions the 'unforeseen circumstances' (while article 9 mentions nothing at all). Thus article 11 might be applicable here. Giving two of the remixers an alternative price is the solution!
And oh, a competition is clearly a contract too, there's a consent between several parties. Who told you that this aint the case?