Percentage-off coupons apply to the reservation's accommodation fare. If the original accommodation fare is changed, the coupon amount will be applied based on the updated accommodation fare.
For example, a 10% off coupon is applied for a listing with a nightly accommodation fare of $100. A guest booked a reservation for the listing, with the coupon applied. You then make a price adjustment to the accommodation fare of your listing to be $150 per night. The 10% off coupon will apply to the updated accommodation fare price, $150.