Revision in salary structure - is it allowed to reduce the fixed component to increase the variable?

Dear Team, I hope most of you are aware about revision of salary structure in some of the IT companies from 90:10 to 70:30 (fixed:variable). My company is also planning to follow the same.
As per my knowledge, we can't reduce the fixed salary to increase the variable component as it's against the law. But I am not sure how other companies are doing it. Can anyone please advice me on this, is it allowed to reduce the fixed component to increase the variable?

Commonly Follwed Precedence is to Implement Any Change with Propective Effect Not Retrospective Effect for the Terms & Conditions of Employment being in the Nature of a Contract, Executed between the Signatories Need to Be Honoured. Trust Deficit is Bound to Tarnish Trusworthiness.
These are my StandPoint I espoused whereever I aided and Advised the Employer/Management.
Harsh K Sharan
Kritarth Team,
1 Dec 2019