Change in rate of depreciation on fixed assets

As Per AS-6 Depreciation Accounting, A change from one method of providing depreciation to anotheris made only if the adoption of the new method is required by statute or forcompliance with an accounting standard or if it is considered that the changewould result in a more appropriate preparation or presentation of the financial statements of the enterprise.

So if change satisfies any of teh criteria mentioned above then only it can be changed.

Yes. If the change in method of depreciation is done as per AS-6 ,it will amount to change is accounting polciy and it requires disclosure in the financial statements.