Very good question for an attorney familiar with TN laws or post the question in the TN forum.
You also need to have an attorney review both loan contract lanquage. It is very unlikely IMO that you can arbritarily charge the $1200 to the real estate loan. And even if you can, and this is the borrower's primary residence, you are increasing your security interest and the ROR will come into play.
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The opinions expressed are mine and they are not to be taken as legal advice.