The terms of the loan would allow you pay off at any time. That's fine. Ethically, it's exactly like paying off your credit card at the end of the month instead of making the minimum payment. Or paying off your mortgage when you have the cash.
I once got a long-term mortgage and paid it off in full within two months. The contract of course allowed me to do this without penalty. But in this case I told the underwriter that I would be doing exactly this. They were still happy to underwrite my loan.
Personally, I would rather tell the lender the truth in this instance. If they don't want my business as a result, then I want to know this information, because it affects my purchasing decision.