your find £28 is just an admin fee or £18 quid admin and £10 for the shear hell of it
if you dont declare any mods you have doneand have an accident thay will void the policy,you will also geta declined/fraud marker on you record and that makes insurance next to impossable to get
Always best to tell your insurace company everything; confirm by e-mail and file a copy.
I fitted headlamp protectors to my old car and told the insurance company who wanted a £15 'admin fee'. I pointed out that fitting these would reduce their risk as the stone or whatever would break a £20 piece of plastic rather than a £300 headlamp unit. They saw common sense, but it's always worth telling them.