Alot of enduros are registered under power from factory, they can be riden on A2 however if police decide to Dyno you it can cause issues. My mates Beta 300rr came brand new registered at something like 11kw, and I have seen alot of the KTMs are the same. Some insurers ask for proof of restrictions with a2 bikes, most don't. It's on you wether you want to risk it or not, however the likelyhood, atleast in the UK, of being convicted seems fairly slim, I know alot of people riding 600s, KTM 690 unrestricted etc on A2 with no issues, but in the event of a crash you may not be paid out, but the same goes for not declaring modifications. Insurance nowerdays is a nightmare, it's up to you how you want to go about it all.