If I opt for a lump sum from my ex-spouse, can I ask for a modification should my circumstances change?

No, you may not. Lump sum alimony is the only maintenance payment that cannot be modified. Once a lump sum has been agreed upon, you or your ex-spouse cannot change it, no matter what the circumstances. For this reason alone, it is imperative that you consult with your lawyer and financial advisor about any lump sum alimony. Agreeing to an inappropriate lump sum settlement can be a severe financial mistake.