Both the Constitution of the United States and the Michigan Constitution have crystal-clear prohibitions against ex post facto laws:

No bill of attainder or ex post facto law shall be passed.  (U. S. Constitution, Article 1, Section 9)

No bill of attainder, ex post facto law, or law impairing the obligation of contract shall be enacted.  (Michigan Constitution, Article 1, Section 10)

This charter amendment, as it is currently written and according to the Kentwood City Counsel, amounts to an ex post facto law that is intended for enshrinement in the city's charter.

I intend on raising that point tonight at the commission meeting.  For a change, probably because there's already some public backlash developing against this amendment, the commission is going to forego the "executive session" portion of the scheduled meeting and handle the entire matter in the form of the committee of the whole.