Numerous bounties have as of now says it all in their standards and guidelines that BM can change the rules anytime so bounty hunters should realize that changes can occur anytime aswell
Anytime does not mean they (company, ICO team) can change rules after bounty is over and work is done. Imagine that you are bartender, you arrange deal with your employer for $500 per month, after a month of hard work your employer gives you $10 and say, I change rules of our deal because I can do that. You wouldn't blame yourself in this situation.