If my wife and I agree on a lump sum payment, can she ask for a modification should her circumstances change?

No, she may not. Lump sum alimony is the only maintenance payment that cannot be modified. Once a lump sum has been agreed upon, you cannot change it, no matter what the circumstances. For this reason alone it is imperative that you consult with your lawyer and/or financial planner about any lump sum payments as alimony. A lump sum payment typically carries with it a financial sacrifice.