When a divorce agreement is submitted, whatever is contained within that agreement is ratified and becomes court order, so yes, there is an order for child support.
Child support amounts are modifiable based on earnings/income.
What does the divorce agreement specifically say about child support? The exact wording would be helpful. Typically, because it was established in NY, then even if parties move, the agreement still holds true. For example, if the agreement says child support in the amount of xx per month based on NY guidelines (which do go up to the age of 21), the amount can change, but not typically the age at which it ends. Just because the parties move, does not mean that original agreement does not hold true. If that was the case, people would move to NY all of the time to have child support extended to the age of 21 or vice versa, people would move out of NY hoping to change the age they have to stop paying support. NY is where the order was established and those guidelines need to be followed.
What is the motive here??