You'll often want to adjust some aspect of the OSD during testing if a prelaunch script needs tweeking for example.
To get directly to the "active" OSD for editing carry out the following:
Launch the App-V Client and locate the item in the Applications Folder.
Right click and select properties and copy the Local OSD File string value to the clipboard.
Open Notepad with admin rights.
File_Open paste in the OSD location you copied earlier.
You can now make your edits and save before testing the effects during launch by activating the shortcut.