Borrower wants to pay significant portion of down

[James Palassis]

I am the lender on a 3 year loan with a balloon at the end, we are 14 months into it. My borrower came to me today to see if I would accept a $50,000 principal only payment, representing about 50% of the total loan amount. I am good with the paydown, but normally I would keep the payment amount the same and just adjust how much is going to principal and interest each month. My issue is, he wants the payment to be reduced roughly 50% to reflect the lower principal amount. 

I have worked with this borrower many times, never been a day late on payments. But I want to make sure I'm protected. Is the move here to get a new promissory note through a real estate attorney? Could I draft my own note and have each party notarize the new terms of the loan?

Any help or suggestions are greatly appreciated!