Reviewing the user override options tip at Tip - Action Override User settings may be helpful.
Consider that by default the process launches in 32-bit mode, so you may need ‘action uses wow64 redirection false’ in the actionscript, else the registry values may end up at HKCU\Software\Wow6432Node
Consider that the spawned process, running as a standard user, probably does not have access to the ‘BES Client\__BESData’ folder, and your .reg file, script, or executables may need to be stored elsewhere.
Likewise, you may need the spawned shell to explicitly ‘cd’ to a folder the user can read, to use as its “current working directory” - i.e.
wait cmd.exe /c “cd C:\windows\system32 & reg.exe add “HKCU\Software\MyTestKey” /v “MyTestValue” /t REG_SZ /d “This is my test” /f”