Can a judge change a signed, notorized, divorce stipulation?

It depends on the rules in your state. I ume you are asking for the 2009 tax year, since filing married/joint for 08 would make this a moot point. It's unusual for a judge to do something like that if the parents have already come to an agreement, but your state laws may require it. In some states the custodial parent claims the child, no matter what. In others, if there is joint custody they alternate years. Rarely does a noncustodial parent get to claim the child because there are legal stipulations for how long during the year he has to live with you in order for you to be able to claim him. You should take a look at the IRS website and see what they have to say, then take a look at your state's regs. The judge might have just been changing it because your arrangement wasn't in line with the law.