Modifying imageres.dll in System32 to change icons, not working.

I don't know if this belongs in customization, but since it's modifying something visually I thought I would put it here.

Anyways, back to the problem. I modified imageres.dll in System32 and SysWOW64 to change some of the default icons, but every time I restart to see if it takes effect, both dll's reset. They hold the default icons instead of the ones I used. So, does anyone know why this is happening?

(Edit) I would like to add that I have took ownership of both dll's, and can successfully modify them. The problem occurs when I restart, and it wouldn't take effect unless it was restarted. So I'm kind of stuck here.

And I use Resource Hacker to modify the dll's, if that is important.