engineer certificates

[surfabusa]

i have made the choice to go down the road of turbo's
I am just wondering after reading another thread about laws and mods

i see a lot of bikes here have small mods such lighting,rear sets,lowered,raised etc
then more noticable mods such as turbos,single sided and extended swingarms, 300 and 330 tire kits etc etc

1. how legal are these mods
2. can you get engineer certifcates for them, if so where
3. will insurance companies accept insurance of these mods with /without engineer certificates

thanks in advance to those who reply