154 in relation to 143(3)

A.O disallows certain expenditure say Rs.1,00,000 in notice u/s.143(2). During proceedings of sec.143(3), being auditor I represent my client and A.O agrees to allow 30,000 expenditure and disallow remaining rs.70,000 and pass order u/s.143(3) as concluded. Now again based on Supreme court judgement he want to disallow 30,000 which previously allowed in 143(3) by passing order u/s.154. I concluded that it amounts to change of opinion and hence he can not issue order u/s.154 instead he should issue order u/s.263(Revision order), is my contention valid?