Legal Question in Banking Law in India

It depends upon service conditions and/or offer documents given by Bank. If there is a provision in the promotion letter or in any circulars iaasued by the Bank, that within this much period after the date of offer letter, the candidate can refuse promotion and opt for reversion to earlier cadre and if that period is not elapsed then you can exercise that option. Otherwise if acceptance given is irrevocable nothing can be done except to resign from the Bank.

Once you have accepted the position, generally demotion is not given. You may still apply.