Other than that, you can withdraw principal contributions at anytime without a penalty and the principle and what you earn on the account is tax free. (thecollegeinvestor.com)
It is a good idea to monitor this, especially if additional principal contributions are being made to pay off the loan early. (marthamay.com)
In addition, you can withdraw principal contributions (but not gains within the plan) without penalties or taxes any time you want. (stockmonkeys.com)