If you cancel a booking for which you used a Coupon Code, you will not be able to use the same Coupon for another booking.
If you change a booking for which you used a Coupon Code, you will only be able to use the Coupon Code for another booking if the value of the booking is greater than that of the initial booking. If the value of the final booking is lower than the initial one, you will not be able to use the Coupon Code for the final booking.