Short answer. No, not by simply signing a new one. A modification of the marriage settlements is valid only if made before the celebration of the marriage. After the wedding the property regime changes only through the specific court-supervised routes the Code itself provides, and not by private agreement between the spouses.
What the law says
In order that any modification in the marriage settlements may be valid, it must be made before the celebration of the marriage
Family Code, Article 76 — Modifying Marriage Settlements Before the Marriage. Read the full provision →
What the law says
The spouses may jointly file a verified petition with the court for the voluntary dissolution of the absolute community or the conjugal partnership of gains, and for the separation of their common properties.
Family Code, Article 136 — Voluntary Dissolution on Joint Petition. Read the full provision →
The wedding is the deadline, and it is absolute
Article 76 is short and unusually blunt. For a modification of the marriage settlements to be valid it must be made before the celebration of the marriage. Not merely unenforceable, not voidable at someone's instance — invalid. That means a document the spouses draft, sign and have notarised after the ceremony does not change their regime, however carefully it is worded and however genuinely both of them meant it. Couples who discover after a year or two that absolute community does not suit their circumstances routinely try to fix it this way, and the fix does not work.
Why the Code is this rigid
The property regime is not only the couple's business. Suppliers, banks, buyers and other creditors deal with married people on the strength of what regime governs them, because that determines which assets answer for a debt and whose consent a transaction needs. If two spouses could rewrite that at will, a creditor's position could be altered after the fact by a private document it never saw. The pre-marriage cut-off keeps the regime knowable from the outside. It is the same reasoning that runs through the rest of the Code's property provisions, where creditor notification is a recurring requirement rather than a formality.
The exits the Code does allow
The article is expressly made subject to a handful of other provisions, and those are the real post-marriage routes. Spouses who have reconciled after a legal separation may agree to revive their former regime, under oath and with court approval. A spouse abandoned without just cause, or whose partner has failed to comply with obligations to the family, may petition for judicial separation of property. Specific causes such as civil interdiction, judicial declaration of absence, loss of parental authority, abuse of the power of administration, or a year's separation in fact with reconciliation highly improbable will also support a decree.
And the one that needs no fault at all
There is also a consensual route, but it goes through a courtroom rather than a notary. The spouses may jointly file a verified petition for the voluntary dissolution of the absolute community or the conjugal partnership and for the separation of their common properties. All creditors of the regime, and the personal creditors of each spouse, must be listed in the petition and notified of the filing, and the court is directed to take measures to protect them. So the answer to ‘can we change it by agreement?’ is really: your agreement is the beginning of a petition, not a substitute for one.
Related provisions
- Family Code, Article 76 — Modifying Marriage Settlements Before the Marriage
- Family Code, Article 136 — Voluntary Dissolution on Joint Petition