Well, jurisidiction and modification are actually two different things...
Simply put...(this applies to support orders)
If state A initiated the order, it will have continuing control of that order, meaning, the laws of state A will prevail.
If both parties are out of state A, one parent in state B and one parent in state C, the states where that parent lives has jurisdiction over that parent.
Modifying a support order, while the laws of state A apply, can be done in either state B or C.
Going through this right now.
Custody/visitation orders can have jurisdiction changed to where the CP and the children reside, and I believe 6 months is the residential requirements.
I'd always consult an attorney to see what the "low down" on this all is...