I found the reference to license plates front and rear in the new law:
Artículo 165.- Exhibición de las placas. Todo vehículo de motor portará sus placas colocadas en las partes delantera y trasera. No podrán estar ocultas, ni ser impedida su visibilidad con objetos de carácter ornamental o de otro tipo. La placa trasera deberá estar alumbrada por luz incolora o ser de material retro-reflectivo.
Article 165.- Display of the plates. All motor vehicles shall carry their plates on the front and rear. They can not be hidden, nor be prevented from visibility with objects of an ornamental or other nature. The back plate shall be illuminated by colorless light or be of a retro-reflective material.
I can't tell if this is actually a new requirement of not, but it pretty clearly spelled out.