hi! it may be safe under certain scenarios.
in general you can enter into some sort of "contract to sell/assign" with the buyer before executing the transfer of rights or assumption of balance (may be done through a deed of assignment). for your safety, this second step (actual assumption of balance) should be pursued if and only if the 3rd of 3 checks has cleared in your favor.
it is best to confirm assume balance policy (for qualification and process) of the developer as this may vary. the account officer may also have some helpful insights about the proposed arrangement.
hope this helps. good luck!