For the property tax deduction or credit on your 2018 New Jersey tax return you enter the full amount of 2018 property tax that you paid, even if you prepaid some of it in 2017. No override is needed. The New Jersey interview asks you how much property tax you paid. If it's pre-filled with the federal amount, just delete it and enter the correct New Jersey amount.
For 2018 the maximum property tax deduction on the New Jersey tax return is $15,000, so entering more than that is not going to make any difference in your tax return, with or without the prepaid amount.