Difficult question. I feel you would lose FTB TRS - also possible stamp duty implications.
You could avail of the rent a room scheme if you live in the house yourself and rent some of the rooms out. Maximum rent €7,620. Go €1 over and all is taxable. From this you may also lose at least some of the TRS and indeed may have stamp duty implications. Stay below this rent and you can get full TRS, no CGT on subsequent sale, etc.. Dependant upon the detail my advice is either move into it or else leave it empty until you are ready.