Generally speaking, yes, any contract can be modified by a subsequent contract (i.e., an addendum to the existing contract).
What the term "incorporated but not merged" means is that the agreement is incorporated into the order of the court as if each word in the agreement were set forth (restated) in the court order BUT THAT the agreement does not disappear into the court order (is not merged into the order), which means that the agreement remains both a separate contract (modifiable and enforceable to the same extent as any other marital agreement contract) and a court order (modifiable and enforceable in the same manner as any other domestic relations court order).
Once the contract is properly and validly modified by addendum, the addendum should be submitted to the court with a consent order (assuming that the court's jurisdiction to enter such modification order was properly reserved in the original final order). You need to have an attorney review this with you and prepare the proper documents. I would strongly encourage against trying to monkey around with these types of modifications on your own.
This response does not create an attorney-client relationship and is intended for general information purposes only.
If the parties agree to change it. If it is child custody or child support and there has been a material change of circumstances. If there is a provision in the Agreement that something can be changed. In other words, it depends. Consult an attorney who can review the particulars of your Agreement.
This response does not create an attorney-client relationship and is intended for general information purposes only. For specific information regarding your case, call my office at 757-533-5400 to schedule a consultation.
If the agreement provides for amendment within it's terms then the amending power is part of the court order and the agreement should be able to be amended. You may need to return to court to have the amended provisions incorporated into a new court order for enforcement. Frankly, this is a great question but I don't have the time to research the issue of "incorporating the amended provisions for enforcement purposes".