I did not do a Post-Nup, but I drew up a 'Marriage Contract' right after DDay and I decided to R.
We reviewed it, made some changes and fWW didn't like the contract word, so we changed it to "Marriage Pledge". It talked about boundaries, consequences of broken promises, handling conflict, date nights, etc.
At least it put the items on the table and we agreed upon them. She has broken some of them since (mostly lying)and I have to remind her of the pledge, and then she gets it.
I don't think it's a legal document but it helped me/us.