If something is done that is contrary to what the prenup was supposed to clarify such as separate property or any other clause. Would the prenup be of no use in court? How might it be judged?
The prenup is not voided by such actions.....merely that the definitions of "Separate Property" and "Marital Property" will define certain assets that used to be separate as now being marital. If you want to fix the problem then amend the prenup (now a post-nup) and rejigger the assets/accounts to get them back into place where each party wants them to be so as to prospectively have it all in proper order again--assuming both parties are willing to do this.
My answer is not intended to be giving legal advice and this topic can be a complex area where the advice of a licensed attorney in your State should be obtained. Please click "helpful" or "best answer" if my answer added any value or add a "comment" if you have more info for me to help you get a better answer.
This question cannot be definitively answered without a review of the agreement.
* If you found my answer to be "HELPFUL," or the "BEST ANSWER," please feel free to mark it accordingly.