bmi diamond club - Change Zone on Redemption Booking?

Any experience on how strict the call centre is wrt the T&Cs quoted below?
I would like to add a sector to an already ticketed award booking. Have BKK-SIN-MEL-AKL and would like to add HKG-BKK, or possibly do HKG-SIN instead. Mileage requirement is the same for Zone 7 (BKK) and Zone 8 (HKG) to Zone 9 (AKL).


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6. booking award flights
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7. Changes to award (or part payment award) flight bookings with bmi or any other partner airline are permitted (subject to the Terms and Conditions) not less than seven days prior to outbound departure only, (providing travel is within the same zone) and will incur a charge of £20 per passenger, per change request (regardless of the number of changes). Changes are not permitted within seven days prior to outbound travel or after travel has commenced.
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Any experience on how strict the call centre is wrt the T&Cs quoted below?
I would like to add a sector to an already ticketed award booking. Have BKK-SIN-MEL-AKL and would like to add HKG-BKK, or possibly do HKG-SIN instead. Mileage requirement is the same for Zone 7 (BKK) and Zone 8 (HKG) to Zone 9 (AKL).In my experience they will not allow any change to the Origin of the ticket - but you could cancel and start over if there are still seats available.

I have had changes made to both origin and destination of redemptions, however I'v eonly tried changing to/from the same zone. Always requires a supervisor though, and even then some sups. won't do it.

If at first you don't succeed, try, try again! :)

How about if wanting to change from Business to First if new inventory is released - are Diamond Club strict on the 7 day rule?