Discover everything you need to know about Texas separate property agreement forms in this engaging and comprehensive blog. This is a document through which the parties agree that particular property will be "separate property" and will not be divided.There is no dispute on appeal that the Marital Property Agreement is a "partition or exchange agreement" within the meaning of section 4.105. 4 M.B. now alleges that the agreement does not address these interests, and thus they constitute undivided marital property. As reflected in the Mediated. The terms of such an agreement are "just and right. "3 The parties obtained approval of their agreement in the 324th District Court of. Exchange Agreement or Postnuptial Agreement.