In some countries mixed systems, i.e. pedaling and/or using a throttle is legal. In EU countries and Switzerland this is not the case. I.e. you can buy an electric scooter, but this is not considered to be an e-bike in the moped / light scooter category. That kind of hack is probably more difficult, unless the original design has been modified to fit with (s)Pedelec specs. E.g. The Ezee models are of that kind and modifications to revert to the original does not seem to be too difficult...
E-bikes are zero-emissions vehicles, as they emit no combustion by-products. However, the environmental effects of electricity generation and power distribution and of manufacturing and disposing of (limited life) high storage density batteries must be taken into account. Even with these issues considered, e-bikes are claimed to have a significantly lower environmental impact than conventional automobiles, and are generally seen as environmentally desirable in an urban environment.[65]

Even the humble bicycle hasn't escaped the clutches of modern technology. A whole herd of new e-bikes with electric motors are taking to our cities' streets. Adding a motor to a standard cycle does ramp up the price significantly, but it takes much of the effort out of cycling, making your commute to the office a sweat-free experience and allowing you to sit back and enjoy your suburban cruise.
Haibike ships the HardNine with 29-inch tires, 180-millimeter hydraulic disc brakes, a 100-millimeter front suspension fork, and a nine-speed Shimano shifting system. The bike’s LCD readout is affixed to the handlebars and displays the current speed, level of charge, remaining range, and current pedal assist mode. The company says the battery can be completely recharged in just four hours, minimizing downtime between rides.

In Quebec power-assisted bicycles are often classified similarly to standard pedal bicycles. They do not have to meet the conditions defined within the Canadian Motor Vehicle Safety Regulations (they are not classed as "motor vehicles"), but they do have to comply with federal regulations that define Power Assisted Bicycles. The Quebec Highway Safety Code defines a power-assisted bicycle as a bicycle with an electric motor. PABs are permitted on the road in the province of Quebec.

Maryland defines an "electric bicycle" as a vehicle that (1) is designed to be operated by human power with the assistance of an electric motor, (2) is equipped with fully operable pedals, (3) has two or three wheels, (4) has a motor with a rating of 500 watts or less, (5) and is capable of a maximum speed of 20 miles per hour on a level surface when powered by the motor. (Senate Bill 379, approved by the Governor 5/5/2014, Chapter 294.) [96] This legislation excludes "electric bicycle" from the definition of "moped", "motorized minibike", and "motor vehicle", and removes the titling and insurance requirements required for electric bicycles under prior Maryland law.
Beginning January 1, 2017, manufacturers and distributors of electric bicycles will be required to apply a label that is permanently affixed, in a prominent location, to each electric bicycle, indicating its class. Should a user "tamper with or modify" an electric bicycle, changing the speed capability, they must replace the label indicating the classification.
Pedelec is a European term that generally referred to an electric bicycle that incorporated a torque and/or a speed sensor and/or a power controller that delivered a proportionate level of assist and only ran when the rider pedaled. On the opposite side, a Noped is a term used by the Ministry of Transportation of Ontario for similar type vehicles which do not have pedals or in which the pedals have been removed from their motorized bicycle. Finally, Assist Bicycle is the technical term used to describe such a vehicle and Power-Assisted Bicycle is used in the Canadian Federal Legislation, but is carefully defined to only apply to electric motor assist, and specifically excludes internal combustion engines (though this is not the case in the United States).
More powerful pedelecs which are not legally classed as bicycles are dubbed S-Pedelecs (short for Schnell-Pedelecs, i.e. Speedy-Pedelecs) in Germany. These have a motor more powerful than 250 watts and less limited, or unlimited, pedal-assist, i.e. the motor does not stop assisting the rider once 25 km/h has been reached. S-Pedelec class e-bikes are therefore usually classified as mopeds or motorcycles rather than as bicycles and therefore may (depending on the jurisdiction) need to be registered and insured, the rider may need some sort of driver's license (either car or motorcycle) and motorcycle helmets may have to be worn.[14] In the United States, many states have adopted S-Pedelecs into the Class 3 category. Class 3 ebikes are limited to <=750 watts of power and 28 mph.[15]
If you are an experienced rider this is actually annoying as hell. Personally, I tend to leave whatever I'm riding in a high gear all the time, because my body is like a powerful machine, and I found the way it slowed my escape from the lights quite disconcerting. For beginners, it could be useful, but it's worth remembering that the whole point of e-bikes is that the motor helps you along anyway, so I do really question the usefulness of this.
Electric bicycle fits under the definition of "moped" under Kentucky law. You don't need tag or insurance, but you need a driver's license. "Moped" means either a motorized bicycle whose frame design may include one (1) or more horizontal crossbars supporting a fuel tank so long as it also has pedals, or a motorized bicycle with a step-through type frame which may or may not have pedals rated no more than two (2) brake horsepower, a cylinder capacity not exceeding fifty (50) cubic centimeters, an automatic transmission not requiring clutching or shifting by the operator after the drive system is engaged, and capable of a maximum speed of not more than thirty (30) miles per hour[94][95] Helmets are required.

An electric bicycle also known as an e-bike is a bicycle with an integrated electric motor which can be used for propulsion. Many kinds of e-bikes are available worldwide, from e-bikes that only have a small motor to assist the rider's pedal-power (i.e., (pedelecs) to somewhat more powerful e-bikes which tend closer to moped-style functionality: all, however, retain the ability to be pedalled by the rider and are therefore not electric motorcycles.

The rest of the bike is equally impressive. Integrated lights in the front and the rear run directly off the main battery, so you’re never replacing coin cells or AAA batteries. And the disc brakes give you plenty of stopping power. The 36-volt battery attaches to the down tube and is designed to be easily removed for recharging. A key-lock at the top of the mount ensures that no one can steal your battery if your bike is left in a public place. And a built-in alarm system, activated with a car-like key fob, is ear-splitting enough to keep thieves away altogether. (Miller promises the alarm’s sensitivity is tuned so it shouldn’t go off if the bike is jostled at a public bike rack, but I didn’t have the bike long enough to test this out.)
The federal Consumer Product Safety Act defines a "low speed electric bicycle" as a two or three wheeled vehicle with fully operable pedals, a top speed when powered solely by the motor under 20 mph (32 km/h) and an electric motor that produces less than 750 W (1.01 hp). The Act authorizes the Consumer Product Safety Commission to protect people who ride low-speed electric vehicles by issuing necessary safety regulations.[63] The rules for e-bikes on public roads, sidewalks, and pathways are under state jurisdiction, and vary.