Wat I meant was "I don't think you can change the icon in Avast file". I believe there's no standalone Avast icon file, the icon is inside one of the binary (or even executable) modules - so if you were to modify the file, you'd corrupt the digital signature of the file, so you most likely would have to disable (and keep disabled) Avast self-defense, and you may also have to disable Microsoft Antimalware process protection (plus, if you want to have a rotation icon, you'd need to have a new icon with all the rotating positions)... I don't think it's really worth it. Furthermore, unless you'd add an "external" signature to the folder, Avast installer/updater would probably revert the change rather soon.
Can't rule out the possibility that there exists a tool that can control tray icons (put its own there, and forward the mouse-triggered messages to the original application)... don't know, just speculating.