Able to revise project budget less than the actual cost imported to project

Summary:

The budgetary control is enabled at absolute level for project budget and project budget was created for example of amount 10000 USD and actual cost is imported to project is 8500 USD

Now business is revising the budget to 8000 USD and system is allowing to revise project budget less than the actual cost

Is there any control or validation that can be developed to restrict the users that shouldnt to reviese the budget less than the actual cost.

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