Search notes:

Registry: HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Applets\Regedit\Favorites

HKEY_CURRENT_USER\Software\Microsoft\Windows\CurrentVersion\Applets\Regedit\Favorites stores the favorites of regedit.exe.

Adding some favorites with PowerShell

It's possible to add some favorites with PowerShell. The script creates the registry key Favorites if it does not exist: 
if (-not (test-path HKCU:/Software/Microsoft/Windows/CurrentVersion/Applets/Regedit/Favorites )) {
   $null = new-item -force HKCU:/Software/Microsoft/Windows/CurrentVersion/Applets/Regedit/Favorites
}

$null = set-itemProperty HKCU:/Software/Microsoft/Windows/CurrentVersion/Applets/Regedit/Favorites -name regFavorites -value 'HKCU\Software\Microsoft\Windows\CurrentVersion\Applets\Regedit\Favorites'
$null = set-itemProperty HKCU:/Software/Microsoft/Windows/CurrentVersion/Applets/Regedit/Favorites -name userEnv      -value 'HKCU\Environment'
$null = set-itemProperty HKCU:/Software/Microsoft/Windows/CurrentVersion/Applets/Regedit/Favorites -name machineEnv   -value 'HKLM\SYSTEM\CurrentControlSet\Control\Session Manager\Environment'
Github repository about-Windows-Registry, path: /HKEY_CURRENT_USER/Software/Microsoft/Windows/CurrentVersion/Applets/Regedit/Favorites/add-some.ps1

Index