After the date of your marriage, you can make new agreements, though not by amending your prenuptial (premarital) agreement.
New agreements would be in the legal document known as a post-marital (post-nuptial) agreement. A post-marital agreement requires similar disclosures so you and your spouse will need to exchange full and current financial disclosures with each other.
So long as you have not mixed your inheritance funds with family funds/expenses, you should have no trouble categorizing it as separate property. However, if upon receiving the inheritance, you bought a new family home using proceeds from the sale of a prior home combined with part of the inheritance, you need to carefully find out where all of the funds came from and what you intend to happen to them in the event of a divorce. This ‘comingling’ and ‘tracing’ are some of the most expensive and most litigated matters in family law. A post-marital agreement will identify the inheritance and manage the expectations of both spouses. This saves emotions and finances for you and your spouse.
Please know that there is a higher standard in preparing a post-marital agreement than a pre-marital (pre-nuptial) agreement because at the time of a post-marital agreement you are already married and you owe each other a fiduciary duty due to the marriage relationship. Prior to the marriage, you can always decide not to get married. Once you are married, new agreements need to be fair for both spouses under their circumstances.
Discussions with your spouse about new agreements for a post-marital document can be tough. However, if your marriage is strong, now is the time to address these concerns with your spouse so unintended consequences don’t haunt you and your family in the future.