@Dion DePaoli
I appreciate your cautious tone as it affirms that to enter such an agreement all parties need to be informed of the risk/reward scenario. I agree that referencing Investor A as a Lender is inaccurate. To take this a step further the existing notes are results of a private Seller-financed loan. The Sellers were flexible enough to allow the subordination and substitution. You are correct in that when a seller does agree to allow other property to substitute on the collateral a separate mortgage document is drafted where the original seller (dare I say lender) agrees again to the terms of the original note with a new property serving as collateral.
I do disagree with your assertion:
"Loans purposely do not contain these types of clauses as that would lead to the exact idea you are trying to skirt which is never paying the loan off and transferring the secured interest of the note to new property. "
If you have a 15-year mortgage note that a Seller has agreed to create and the underlying property is being refinanced within a 2-year period of that note's creation, to collateralize the note with another property - how does this equate to never paying of the loan? If the Seller were flexible enough to agree to the note and their only other option is to accept a discounted pay-off, why wouldn't they agree to the same terms where the only change would be property that is serving as collateral?
Caution should prevail. All parties (Investor A, Investor B & original Seller) should be privy to the transaction. To not move forward and leave it alone may indeed be the best option depending on the intent of the parties, quality of the collateral and legality of the agreements.