Unfortunately, Android does not allow changing of the application icon because it’s sealed in the APK once the program is compiled. There is no way to programmatically change it to a ‘drawable’.
You may achieve your goal by using a widget instead of an icon. Widgets are highly customisable and can do what you want.
There’s a short discussion about the difference between iPhone icon notification and using widgets here:
http://www.cnet.com/8301-19736_1-10278814-251.html
As you’ll notice, there is virtually no difference between using a widget or an icon, since they can be the same size and look the same.