When changing the appearance of a part, and saving this appearance as a .p2m file, I can't get other parts with the same .p2m file to update their appearances.

I have a bunch of parts that I want to have the same appearance. If I change the appearance of one part, I want all my other parts to change appearance as well.

The appearance for each of my parts is defined by a .p2m file - let's call this file "aluminum6061.p2m". If I edit the appearance of one of these parts, and save the appearance under the SAME name again (replacing the old .p2m file), I would expect that the other parts update their appearance. After all, their appearances are define according to aluminum6061.p2m as well. However, this is not the case. The other parts don't update their appearances. How can I easily change the appearance of a whole collection of parts, without having to manually edit the appearance of all of them?