the other thing you need to look at are the ADR's. if they state no to something (eg: no lower that xxcm, tint no darker than xx) then you cant get a cert for that item.
The certs are for things that you can change (engines, brakes, half cage etc) that are not with in the manufacturers guide lines.
Its just to say that it was done correctly and that no extra harm will happen to you or anyone else because of said change/s.