Jalil,
As Shaitaan pointed out pensions cannot be stripped willy nilly.
I think this has to pass through Parliament.
One can diminish or even do away altogether with pensions and facilities for future former Presidents by an Act of Parliament.
However, it is not possible for any Bill to have retroactive effect on Jagdeo, Hinds, and Ramotar. They're pretty solid for all time to come.
The only theoretical way to strip Jagdeo, Hinds, and/or Ramotar is by amendment to the Constitution in the hardest way possible. Such a bill cannot even be passed unanimously by Parliament alone but also requires a successful vote at referendum because it alters a fundamental right. So for all intents and purposes, there is no practical legal avenue to undo what's been done by any future Government of Guyana.