Right...unless every other member agrees sans Hungary then they can add that rule. The framework is built on trust and as long as all parties are in agreement the trust remains. If every party wants Hungary gone then Hungary's opinion is moot. If at least one other member were to object though then they would be stuck or risk breaching the trust between member states.

De facto if every EU member except hungarh agreed to the rule nobody would be upset except hungary which tough titties if they already want them out. Any rule is valid if the rest are unanimous on it.