Adding plugins to Upgrades Package

I noticed Brayne's post a while back, and I was wondering what to use for the "xxxxxxxxblahblahblah" part... Can this be any unique made-up string?

Also, it would be great to have the capability to add Themes & Plugins to an upgrade package, just like we can with supporter. Or will it be possible to create different packages for different supporter levels in Supporter v3.0?