regedit.exe does not accept any command line parameters for opening a given key.
there are two ways to determine the Certitification Authority in your Active Directory environment.
search index GUI is not an exe file. The GUI resides in an DLL. To open it you have to call it by rundll32
the executable which shows the the Windows Defender Notification icon in systray or notification area is %ProgramFiles%\Windows Defender\MSASCuiL.exe.
This program is simply started by a run key in HKEY_LOCAL_MACHINE. So if you want that the icon is gone and no longer being shown delete the run key.
C:\> reg delete HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Run /v SecurityHealth /f
If you want it back recreate the key
C:\> reg add HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Run /v SecurityHealth /t REG_SZ /d "%ProgramFiles%\Windows Defender\MSASCuiL.exe" /f
the Internet Explorer is shipped with its own Developer Tools for developing, analyzing or modifing Websites in real time.