Only now did i understand what you want. Right, that makes all sense.
Here's the code in autohotkeys to do what you ask for:
Menu, tray, icon, %1%,1
If you'd like to run it, just download ahk from www.autohotkey.com
. (if you prefer, i could compile it and post the .exe).
All you have to do is call it with an argument. That argument has to be the name of the icon you'd like to use. To change the icon, just run it again with a new parameter, the old version will be closed.