That's an acceptable target, as it functionally gets you to the file you need to test (e.g. trillian.exe)
However, since the Registry Value "DisplayIcon" contains the fully qualified pathname, you should leave Sub-Path empty.
Sub-Path is only defined when you need to complete the relative path to the actual file when the pathname in the registry value is a base folder.
e.g. if the registry value contained "C:\Program Files (x86)\Trillian" then Sub-Path would simply be Trillian.EXE.