"Generally, when you turn 55, you can withdraw at least $5,000 or any amount in excess after setting aside your
Full Retirement Sum (FRS).
If you are born in 1958 and after, when you turn 65, you can withdraw an additional amount of up to 20% of your retirement savings.
See more details on the withdrawal rules."
======
Of course, if what you want to do is to only set aside BRS, you will have to pledge property, that decision must also be made at 55, but that will be a different scenario from setting aside FRS/ERS.
I don't think the system allows you to change your mind in the 10 years from 55 to 65, i.e, FRS at 55 then change to BRS then.