Currently (as of Creo Parametric 2.0) when adding a Command to the Quick Access Toolbar the Command is only available in the module where the Command was added.
For example, when in the Part Design module customize the Quick Access Toolbar and add the 'Activate' command. Switch to the Assembly Design module and notice how the 'Activate' command is not listed in the Quick Access Toolbar. The user must then customize the Quick Access Toolbar again to add the new same 'Activate' command.
It would nice if functionality could be introduced where users can define if the Command is to be made available Globally across all Quick Access Toolbars, versus select modules.