Not want to discourage you in your attempt to license your transformed ICE motorcycle or scooter to electric ( which involves insurance, paperwork, VIN numbers, and possible Certificate of Conformity papers and EMC approval ) but I tried to get some info on this topic, digging deep and hard in Belgium and the Netherlands, but it is pretty much impossible unless you got.
A: Deep pockets, some company, I believe TüV Sud and Dare!! Benelux told me that the EMC alone in order to get the CoC for a single (D.I.Y made vehicle ) would run in the thousands of euro's, I was quoted between 8000 and 12000,- Euro to get my Electrified KMX EMC approved as an electric vehicle, this is of course when I got the test/approval right the first time.....then when this is done, you would need a one-off type approval and get some ( new ) VIN numbers stamped onto your frame, after that you can get your vehicle licensed and insured, and all the other paperwork in order,you can imagine you also need....
B: Incredible patience, you're in for the long haul, this is gonna take endless time and effort to get it right, and if it would be for a manufacturer that is planning to sell 10's of thousands of vehicles in the EU than this is a small turd to swallow, for the Hobby Bob that is fabricobbling his own vehicle in the backyard shed, this is pretty much impossible.
If you want my honest opinion, this needless red tape that the EU is putting up even for one-off's is what holding back the electrification of our continent, some rules need to be in place to avoid accidents and deaths due to some guys that weld a frame together with a stick welder and some car batteries doing 95kmh on a bike trail, but i'm sure that a lot of people know what they are doing and are quite sensible ( on account of seeing so many beautiful and sound creations here on ES )
But unfortunately this is a big boy's game that is being played by large car manufacturers that lobby their asses off in Brussels, they don´t need more competition, thank you very much....just eat what you get on your plate from us. (Signed, the car manufacturers
It will be a long time before guys like Jehugarcia,( see youtube ) to drive around in a electrified VW T1 Samba without a windscreen with his dog on the passenger seat and a bunch of second hand laptop 18650's strapped under the floor, to happen in Europe....