Most federal voting violations are found in 42 USC Section 1973I, including the misrepresentation of information to register and voting more than once. While I certainly do not believe that you will be prosecuted under these facts (based on your intending NOT to be registered in both states), it is worth the stamp to resolve the matter with finality.
Joshua Sabert Lowther, Esq.
NATIONAL FEDERAL DEFENSE GROUP
You may want to send the letter just to end it, but as Mr. Lowther notes, it is unlikely you would be prosecuted unless you actually voted in both states.
This response does not create an attorney client relationship and is offered for informational purposes only. Only a lawyer fully versed on the facts and circumstances of your case can properly advise you on the case. I am licensed to practice in Minnesota, not every state. You should always consult with an attorney licensed in your area on how best to proceed.