How are those involved with enforcement suppose to know the difference?
ebikes are required to have a sticker stating it's class (I, II, III) as well as their top assisted speed. A bike like this can be switched between power modes and although it may have a mode restricting it to 750W and 20mph, it does not meet the requirements. Obviously it's a sticker and you could just make one up that says Class II, etc and most enforcement agencies are unable to tell the difference. In the UK authorities seem better equipped to identify "chipped" and other illegal ebikes.
" b. On and after January 1, 2019, manufacturers and distributors of low-speed electric bicycles shall apply a label that is permanently affixed, in a prominent location, to each lowspeed electric bicycle. The label shall contain the classification number, top assisted speed, and motor wattage of the low-speed electric bicycle, and shall be printed in Arial font in at least 9-point type.
c. A person shall not tamper with or modify a low-speed electric bicycle so as to change the motor-powered speed capability or engagement of a low-speed electric bicycle, unless that person appropriately replaces the label indicating the classification required in subsection b. of this section. "