Yes, you can withdraw your application to the Heritage Lottery Fund and apply to this fund providing you have not already received the offer of a grant. However, you should contact your local Heritage Lottery Fund office at the earliest opportunity to discuss the implications of withdrawing your application.
You cannot apply for a grant from this fund if you have an existing offer for a repair grant from the Heritage Lottery Fund, or from Cadw, English Heritage (now Historic England), Historic Scotland, Northern Ireland Environment Agency, even if you have not yet formally accepted it.