I've been honest and never noticed any great difference on premiums, no accidents

(no seriously)
But if you didnt tell them that COULD make the Policy null and void in case of an accident (surely?).
Likewise if you dont tell them about aftermarket pipes, ignitions etc.
And if they are illegal to start with as well as not being told well you deserve it, not only that you wont get a claim on it (witness $2.5K of c/f).
Dont assume you will be able to put the original on in the case of an accident (as I have heard some wankers say).
a) the bike will be bent, so will the pipes etc.
b) you prob will be too and in no state to change parts
c) you might not even HAVE access to the bike
d) it will prob stand out like dogs if you DO mange to swap it (ie clean dirty etc) unless you have TWO fucked up ones.
e) And finally its called FRAUD if you get caught.
Just my 10c