If the top-up is is being spent on the purchase/renovation/improvement of one's PPR yet. Otherwise no.
It's not how you apply for it it's how you spend the money that counts. Are you borrowing to spend the money on your property? If not then you cannot claim owner occupier mortgage interest relief on the additional amount. If you are then you contact Revenue and your lender to claim the additional relief. Claiming the relief when you are not entitled to it would be tax evasion.