Put all the collateral and debt in a single deed of trust or mortgage. This would seem to be a simple, efficient and logical rule.Future advance clauses are customarily included in Texas deeds of trust (and other Texas security instruments). The mortgage modification agreement is a legal document between a lender and borrower to change an existing loan's terms. Prior Mortgage or Deed of Trust; Modification; Future Advance. SAN ANTONIO, TX 78288-0558. San Antonio 1975, writ ref'd n.r.e.). Put all the debt in a single deed of trust or mortgage. Prior Mortgage or Deed of Trust; Modification; Future Advance. , 677 S.W.2d 480, 481 (Tex.