Most EK Fares contain a rule that you can only change to an equivalent or higher fare:
... A CHANGE IS A DATE/FLIGHT/ROUTING/BOOKING
CODE CHANGE.
... CHANGE FEE APPLIES PER PASSENGER PER
TRANSACTION.
... CHANGE FEE DOES NOT APPLY TO INFANT NOT
OCCUPYING A SEAT.
... CHD/INF WITH A SEAT DISCOUNT DOES NOT APPLY
ON THE CHANGE/REROUTING FEES.
... CHANGE IS PERMITTED WITHIN TICKET VALIDITY OF
ORIGINAL TICKET.
... CHANGES ONLY PERMITTED TO FARE OF EQUIVALENT
OR HIGHER VALUE.
... CHANGES ARE TO BE DONE BY THE ORIGNIAL
ISSUING AGENT OR EK OFFICES ONLY.