Assume only add in all the penalty charges due to extension (less than 10k), the "bumi lot" winning price should be still cheaper than non bumi lot lelong price of the same size.
Taking above 1027sqft unit as an example. Bumi lot unit sold at 311k. Non bumi lot unit will be at least 350k.
1. The correct party to check whether the unit is under bumi lot or not is to get confirmation with the developer. Not bank. Not agent. Not lawyer. If you refer to lawyer, the lawyer will still need to check with the developer. Only the developer holds the answer.
2. POS will not state all information. Depending on which auction bank. Example of important information not stated:
- Bumi lot status
- Strata title issued status
- Final 5% or 2.5% due to the developer (for newly VP property as bank did not disburse this amount due to the borrower start default during progressive interest)
- Number of parking lot for this unit
3. It is possible to still pull out after winning and during name transfer time, got this bumi lot issue. The auction bank will refund you the 10% amount due to their mistake on not stating bumi lot. The unit will be re-auction bank again but the POS will state bumi lot this time. You may go through the POS again. Some banks very clear cut will state in the T&C.
However, any outstanding fees you paid to the management office or legal fees paid to engage lawyer will not be refunded.
Finally, is always a risk in lelong. Hopefully is a happy ending in the end. I mean the unit successfully convert from bumi lot to non bumi.

Only able to answer your first question.
Yes if the property is still under master title, developer still got the power to switch around the bumi lot allocation. Many older property still stuck with master title coz developer oversold and not able to meet the bumi lot quota.

leelianeik if able to share whether any additional cost need to pay? Real case study.

And for your last question. No, is not possible for non bumi to bid for bumi lot unit. The auctioneer will reject if a non bumi register for a bumi lot unit. For some banks, even your represented agent (to bid on behalf) must be bumi if you are buying bumi lot unit. Non bumi agent with authorization by bumi buyer is not allowed to bid on behalf.