Fd cash accounting method

Hi,

I am a salaried individual and wanted to your expert opinon for few questions.

1. I have been following accrued accounting method (mercantile) for Income from other sources like FD till date.
    I want to shift to cash accounting method from this financial year and in future.
    What documentation should I keep handy to indicate that I have changed the accounting method?

2. Assume I have a cummulative interest FD (ie. payable at maturity) which matures in Jan 2014.
    I reinvest the entire amount(principal + interest) to create new FD with the same bank.
    In the above case, can i treat the interest as "receipt" basis so that I can tax the amount when the new FD matures?

3. In case of cash accounting method, do I need to pay advance tax as applicable. My understanding is NO since
    the interest is taxable on actual receipt basis.

4. In there any timeframe or conditions which I need to satisfy to back to merchantile method in future?

Thanks in advance.