Unruly Icons

Hello All
I have been experimenting with the icons on my Windows 7 desktop.
I have learned quite a bit, but I have a problem I cant solve.
Everytime I change one the icons on one of my folders they return back
to the original icon after awhile or if I add or delete any of the contents.
Is there anyway to keep the changes permanent ? Also why is it that
some icons don't change, such as app. icons.
Any help will be appreciated.

RalphG