If you put these two blogs together:
You get this sequence of powershell commands, to export a start screen, set it to the default start screen of a device, and revert a user back to the default start screen.
1. export your start screen as a .bin file
Export–StartLayout –As BIN –Path CustomStartScreenLayout.bin
2. Mess up your start screen a little so you can see when you revert to your exported screen
3. Import your saved start screen to your machine’s default profile. This has no effect on your start screen but it does on any new users on your device. I too couldn’t get %SystemDrive% to work, but $env:SystemDrive worked a treat.
Import–StartLayout –LayoutPath .\CustomStartScreenLayout.bin –MountPath $env:SystemDrive\
4. Reset your start screen back to the default profile (ie make it the same as the one you just imported):
ren “%userprofile%\AppData\Local\Microsoft\Windows\appsFolder.itemdata-ms” “appsFolder.itemdata-ms.bk1”
ren “%userprofile%\AppData\Local\Microsoft\Windows\appsFolder.itemdata-ms.bak” “appsFolder.itemdata-ms.bak.bk2”
… and reboot.
Your start screen will now be the one you exported in step 1, and any new users on your device will get your start screen too.