It is not possible to get a 100% loan of the purchase price. All info is on the HDB website.
Do you mean a 2nd HLE/HDB loan for your next purchase or a HLE re-assessment? You mean your 1st purchase is a BTO and you want to get a reassessment when the BTO is in the construction stage? Or you mean you have a HDB purchased already and you are currently occupying it and you have an upcoming BTO and while it's being constructed, you want to get a HLE loan for it?
For new flats, the LTV limit* is up to 90% of the purchase price. For resale flats, it is up to 90% of the lower of the resale price or value of the flat.
https://www.hdb.gov.sg/residential/...hdb/more-information-on-your-hdb-housing-loan
If you have purchased an uncompleted flat from HDB,
we will review your financial position nearer the completion of the flat. This is
to confirm that there is no change in your ability to service the housing loan.
I interpret it as that even if there's an increase in your income, they won't change the loan amount. The review is to ensure your income doesn't get lesser and you lose the ability to service the loan amount.
https://www.hdb.gov.sg/residential/.../housing-loan-from-hdb/eligibility-conditions