Under the Occupier and Owner scheme for a BTO unit, how much are the costs if the Occupier is subsequently added as the Owner for financing purposes? Heard there will Stamp Duty but unsure if it's 2+%?

Do you mean changing a spouse from an occupier to an owner? If so, it just requires that the person becoming an owner get an HLE letter (if there's an outstanding loan). After that there's a three month process with fees of up to $1k to add the person as an owner.