You want to get a prenuptial agreement, and your significant other has agreed to it. Your only concern, though, is simply setting things in stone when your lives may significantly change in the years to come. Can you alter the prenup at a later date, or are you stuck with whatever you decide today?
You can change it. The main thing to note is that both you and your spouse have to agree. You cannot change it on your own.
To do it, the easiest way is to revoke the prenup that you have and then draft a new document that addresses your new circumstances. You and your spouse can work together to decide exactly how the new document -- which is now a postnup if you got married -- can address your needs moving forward.
Many couples also choose to put timers on their prenups. For instance, you may draft a document that only stays valid for the next decade. It automatically expires in 10 years, and it no longer applies. You can then decide if you want to draft a new document or simply continue on without one.
One big reason for these expiring prenups is that people fear losing assets after a quick divorce. If they make it to 10 years, then they figure the marriage is going to last -- even though it may not.
As you can see, you have a lot of options when creating a prenup. Make sure you understand exactly how they work and what legal steps you will need to take.