Not so much an exception but a work around according to the guardian newspaper [1]:
[...] the law specifically says “no head and shoulders portrait or bust of any person, living or dead, and no portrait of a living person may be included in the design on the reverse of any coin “created to mark the US anniversary”.
The proposed design features a wider illustration of Trump on the reverse side, a move that legal experts said would fall outside the ban on a “head and shoulders portrait or bust”.