I had a need to add a certain security group to every single published application in a XenApp 6.5 farm today. Create a new file with the extension .ps1 and copy and paste this in:
foreach($application in Get-XAApplication)
Add-XAApplicationAccount $application.DisplayName "domain\yoursecuritygroup"
Then run the PowerShell script. It will enumerate all apps in your farm and add the security group or user ID you specified to each app. Don’t worry, it won’t overwrite any existing users or groups for the apps, it will only add.
When you check the app properties now, you will see the new group added to all apps. Hope this helps!