The suits currently dampens powers to 20% of their effectiveness, yes! If once granted magic Nyx no longer requires the crystal or King Regis (as in, the power is independently his own without needing to be recharged or channeled from the crystal itself), then that power will stick with him.

If it is a power which requires the crystal to exist in the same universe as him to use, then he will unfortunately be out of luck and still unable to use it.