I was trying to edit the icons to X applications when I noticed that the packages were now documents after installing 9.1 (they are no longer folders as they were in OS 9.0.4). Clicking on any of the apps brings up a dialog stating:
The package "program name" could not be opened, because it cannot be used with this version of the Mac OS or there is a problem with it.
If there is a problem with it, try reinstalling the package.
Also when control-clicking on a carbon/cocoa app you will see the Show Package Contents option in the contextual menu. I think this is very interesting