The issue will be that the User registry hive is typically only loaded while the user is logged on, so you can only search for the value for the user(s) that are logged on at the time.
Also, HKEY_CURRENT_USER is a symbolic link to HKEY_USERS* where * indicates a match for all user security IDs (SIDs). HKEY_USERS*\SOFTWARE\Classes is a symbolic link to HKEY_USERS*_Classes.
(Registry Keys Affected by WOW64 - Win32 apps | Microsoft Learn)
Also, the Agent runs as local system, which has a different HKCU hive than the user who is logged into the box.
(https://developer.bigfix.com/relevance/reference/logged-on-user.html#user-key-of-logged-on-user-registry-key)
And actioning can get tricky as well:
https://www.ibm.com/developerworks/community/forums/html/topic?id=77777777-0000-0000-0000-000014747943#77777777-0000-0000-0000-000014747944
This Fixlet sample deals with some of these issues and might be a good starting point for you
https://bigfix.me/fixlet/details/767
This forum posting may also help: