No, you cannot transfer Avios (or any airline miles) back to American Express Membership Rewards once the transfer has been completed. All transfers from Amex to partner loyalty programs like British Airways Executive Club, Iberia Plus, or Qatar Airways Privilege Club are final and irreversible. This "one-way street" policy is a standard rule across the entire travel rewards industry. Before you initiate a transfer, it is crucial to confirm that the award seat you want is actually available for booking, as you don't want to be stuck with 100,000 Avios that you cannot use for your intended trip. While you cannot move the points back to your Amex account, Avios do offer a unique level of flexibility because they can be moved freely between the various "Avios-using" airlines (British Airways, Iberia, Aer Lingus, and Qatar Airways) at a 1:1 ratio through the "Combine My Avios" feature. This allows you to hunt for the best redemption rates or lower fuel surcharges across different carriers. However, if you find you have excess Avios that you cannot use for a flight, your only options are to save them for a future trip, use them for hotel bookings, or "gift" them to another member for a fee.