TBH why wouldn't you let your insurer know about any changes

when it's common knowledge that they will look for any excuse to save paying out unless you are with an established Morgan Specialist company who I have found faultless in my dealings with them.
Having said that I don't like bolt on bits and pieces so my changes are just inclusion of younger family members on various occasions over the years.
I agree. If I was having a flash upgrade it would only be sensible to notify it. On the other hand it wouldn't occur to me that thermal wrap on the intake trunking was an insurance issue, but owners wouldn't be doing it unless it was beneficial so arguably a minor performance upgrade. Is it hat type of minor 'tweaking' that may be questionable?
I understand totally where you are coming from and had you have asked me the same question ten years ago I would have taken a far more relaxed approach. The world is a lot more chasing the money these days so yes I would always give the insurance company the option of including any modifications onto the policy nowadays however minor they might appear to us.
I guess an insurance expert is what you need to comment really, if we have one onboard maybe they would like to take a step forward, we can only comment from the end user perspective.