The answer to your query depends on many factors such as the category of the concerned employee likely to be affected by the change, the applicable employment law, the terms of the contract of employment, the principles of wage and salary administration adopted by the management in tune with accepted universal practices in this regard, and the like.
Promotion and Career Advancement
Promotion ensures career advancement for employees as well as the availability of known talent to the organization. From the employee's perspective, promotion, per se, is a kind of career advancement with the upgradation of all the elements associated with higher responsibility.
On the other hand, the grant of a specific allowance available to a higher cadre without advancement means an enhancement of monetary benefits in the context of a practical impossibility caused by the rigid pyramidal structure of the organization, perhaps due to longer experience over time subject to satisfactory performance. In the latter case, it is certainly not a promotion but merely an upgradation to the entitlement of a facility previously unavailable. Therefore, in such a case, common sense would dictate only added advantages and not a reduction in the existing compensation package due to restructuring.
Kind regards