Originally Posted by
Furby
You may be mixing this up with the rule that if you change you flights after booking you can only do so if the new airport is in the same band as the old airport. So no issues as long as you do not later want to change the departure back from Bangkok to Delhi.
Even that was only a rule for the Lloyds upgrade voucher, as it wasn’t returned if a booking was cancelled so they restricted changes within the booked band.
If you’ve booked flights using an AMEX 2-4-1 you can cancel and the voucher will be returned so you can book new flights in any band you wish.