AS-5 is changing of method of depreciation from SLM to WDV is change in estimate or change in policy

Why are you surprised. This gaap accounting is a headache for non ca's. There is nothing we can do apart from following the priciples. I deal with as, indas amd ifrs and I dont feel too good cause i dont byheart and my gist must be 100% accurate. If i take cpa reporting exam, if probably thebclass topper. Policy is a policy and disclosures. Fyi slm is genrally the accepted method. But there is one thingvcalled MODIFIED ACCELRATED DEPRECIATION or something like that which changes the policy and its purely tax planning. 

Itd called as macrs. And its a change in estimate. 

Change in depreciation method is change in accounting estimate.