As a rule, u r only suppose to use the original plates issued by authorities, using any other will violate laws and u will be caught for this offense [using fake number plates].
the plates r the property of the authorities, while it is your legal obligation to maintain them in its original form [material, color,].. you can paint them, provided you do not temper with the color shade, the numbers embossed or any other alternation,
u can also get caught if lets say for exp the isb number plate gets super rusty and becomes unreadable, or the black digits merge into white background..