what if you tell the insurance company of the change of engine and they have it listed on the policy but dont tell the DVLA - technically are you still covered by the insurance?

My saf is going to have an engine change but im not telling the DVLA, as its currently registered as a 2.0 and i will dropping a 2.0 engine back in (albeit with a turbo) - my insurance hasnt mentioned anything to me about it not being covered, in fact i can have whatever mods i want as long as i dont up the engine cc