"You need to use the best answer you have as of this time. The application requires that you notify the marketplace if there is a change in your application, including income. When you file your taxes, a reconciliation will be completed and you will owe any subsidy money you should have not received, but the opposite is also true. If you were owed more money via the subsidy, that will be returned to you. Beyond that, I am not a CPA and can't even play one on TV. You need to contact your CPA."
THAT is the correct answer to the question. Don't game the system. One way or another, you are going to pay the correct amount.
And its not a penalty. Its an adjustment to the subsidy you should have/have not received. There's a difference.
I guess those of us who do this for hundreds of clients a year for virtually nothing in compensation actually do know the system, huh?