In northern New England, it is better to tear off old roof and install a new roof over clean roof deck.

Of course you can use ice melt / rock salt to speed up the process. If it’s just a very thin layer of black ice stuck between the granules on the shingles, you can install the underlayment over it. When the black ice melts, it will be like normal condensation. One thing though – do not use a vapor barrier type roofing underlayment – use roofing felt or better, breathable synthetic underlayment like GAF deck Armor – it will allow the moisture to escape.