Can inform, but subject to insurer if they accept the coverage or not. E.g install ICE rm30k, inform insurance, they'll inspect and look at receipts, ask you questions like where you normally park, etc. then decide to accept the additional coverage or not. If yes, then they'll let you know the extra premium need to pay.

Let's take another example. Car is Wira 1.5. Change engine to 1.6/1.8. Didn't inform insurance. Then accident and want to claim. Insurance can reject the claim since the engine cc in their database is 1.5 and not match physical vehicle. Insurance no need pay single cent.

Just to share, if mod, better do proper way.