In a presentation to the ACS society (Australia), experienced DP John Seale tells of his experience shooting day for night on Mad Max Fury Road. On the advice from his DIT, he overexposed shooting with an Alexa 2-3 stops then graded down. As a film trained DP he had always underexposed but was told this did not hold true with digital cameras and modern grading software.
So shoot a test and see what works best, but do not assume underexposing is the right approach. I have only limited day for night experience and certainly prefer the shot is not underexposed. I want to experiment with 2-3 stops over. It makes sense to preserve shadow detail and just play with grade luma, saturation and cast.