Betting on a block is betting money that effectively says something like:
"I believe that this block has at least a 60% chance of being true."
Q1. Once a bet is made, is it possible to change the bet?
My guess is not, so that initially validators should bet small and eventually they all converge and agree. (Part of Casper is proving this convergence?)
Q2. If a validator has a deposit of 100 ETH (for example), when they make a 10% bet do they put 10 ETH at risk?
Q3. If so, what happens if a validator realizes a mistake and wants to switch and bet 100% on another block? Presumably the 10 ETH will be lost leaving the validator with 90 ETH left for betting. Is that correct or does the validator need to put up another 10 ETH deposit? To bet 100% on another block, does the validator put 90 ETH or 100 ETH at risk?