I know you have to inform insurance companies of modifications but some modifications may be considered too small (eg, a fast-flow filter panel)
Where do you draw the line?
In particular I am interested in the case of fitting a subaru original exhaust part from an STi on to my WRX, and also de-catting pipes (which in principle are illegal on the road anyway).

What about alloys as well, espeacially if they are subaru alloys froma later model??

 

To be safe you should tell them about everything, even uprated panel filters. If they then consider something too small to make a note of, at least your butt is covered.

Different exhausts and roadwheels will definitely be notifiable to the majority of insurers. It doesn't matter whether they're Subaru wheels from a newer Impreza or not, the fact that they're not standard for your particular car is the important thing.

 

So, even platinum spark plugs and stuff like that?!

I just hope the guys from the insurance companies know there stuff and don't confuse that lots of little mods like these with big mods and then charge me loads.