UPDATE: IT WORKS

After sharing my disappointments with 3 cabin service directors (who were all unaware of the Privilege Club enhancements but took notes), I received an email from the privilege Club department.
They profusely apologized for the time it took to address a simple date change request on a biz ticket booked with Qmiles prior to the enhancements.
My request was granted (after being initially refused on the ground of policy change) and funnily enough they ended their message by saying " Do let us know if we can assist you any further. Sincerely"

Needless to say, I'd rather ask the cabin crew directors to forward my future requests to higher management rather than relying on delayed "negative" response from the privilege Club team.

I also learnt one surprising thing from one of the male cabin crew who used to work for the ground services. He was aware of the enhancements and told me that one of the main reasons for the massive devaluation was due to staff abuse with the Qmiles and redemptions.

However I clearly told him that it was a dumb move from the management staff to punish the most loyal customers because of the behavior of some of their staff.