I wouldn't declare consumables, just ensure they are OEM spec and quality.
Other things are a grey area, technically you should declare all modifications, but where is the line drawn? Does s/s brake lines count as a modification? The oem ones need replaced at some point due to being made from rubber, so is replacing them with better more durable ones a modification? If it is, then putting Michelin PSS tyres one us kind of the same, they're better...
The insurance companies should post a list of everything that needs declared and what is considered a consumable/wear and tear replacement.