I am looking to change the icon for the installer file (the native installer not the air). The icons in the descriptor file would be for the application after installation, right ?
e.g if I publish my app over a dvd then I will be putting my exe (installer) on the dvd.. it should show a logo(icon) designed for the app instead of a default (folder like) icon.
Ah I see what you mean now. Unfortunately, this isn't available directly through AIR. However, there are third party utilities on Windows that will allow you to modify the icon resources and it should be simple enough on Mac through File Info.
If you'd like to see this functionality added to AIR, I'd like to suggest you add a feature request to our ideas.adobe.com page.