the fact that you can change the settings means under law it is not road legal no matter what you set it to because you are able to change the settings.Yes, but your post was about the legality, not about how easy it would be to make legal. A BBSHD is one of the easiest systems to convert back to legal - just two screws, one bolt and a ring-nut!
Derestriction, ‘off-road’ switches or modes and dongles
The Department of Transport say that electric bikes fitted with off-road switches or modes, that enable a bike’s motor to continue assisting to speeds beyond 15.5mph, do not comply with UK EAPC law. The term ‘off-road’ suggests that these bikes can be ridden on parkland, forests or other places away from main roads, which isn’t accurate. E-bikes with increased motor power (continuous rated power above 250w) or increased speed (with motor assistance not cutting out at 15.5mph) cannot be used legally as bicycles anywhere on land accessible by the public; when riding on private land you would need permission from the landowner.