Re, nevuah; let’s also be clear that a nevi sheker, even if he just tells you to keep the Torah, is chayav misah. This is a big deal. It’s not just a hashkofa disagreement. What the Lubavitcher rebbe is saying can land one in an aveirah for which the punishment is death.
I think it’s prudent to abide by the pashtus of chazal and mesorah in such a case..if a yungerman had a chidush about shabbos, if he went and told others to be meikil on a chiyuv misa….i shudder to think of the consequences. These are very serious inyonim.