I am 54 years old. If my son tops up my CPF this year, will I be able to withdraw it next year beyond the BRS. And possible to use CPF as a fixed deposit yearly plan to earn interest after 55?

Can withdraw beyond BRS? No, cash withdrawal only allowed if you have FRS. BRS and property pledge are only for those who don't have FRS.

Can treat as fixed deposit? Yes, up to 37k/yr contribution, if MA not max, some goes to MA, then not all 37k will go into OA. If there is balance to do repayment for money used for property and accrued interest, then that's the upper end of contribution limit. However, once withdrawn, you can't deposit the cash back as a savings account.

Short answer. No
Yes, if you done voluntary contribution.

1) The amount is dependent on your FRS.

RSTU (retirement top up scheme) is for your FRS. BRS cannot be used to calculate for this amount. Hence this hack does not apply. Only apply if it is above FRS. Or you just nice have a FRS - 7000. So the amount of money in CPF SA/OA (if you are still working) can be drawn out.

As a fixed deposit interest, yes. Voluntary Contribution can be done (but if your MA has not maxed, it will get stuck in MA)