More tweaks

Activate Windows 10 ARM

To activate, open Windows PowerShell as Administrator and type these commands:

slmgr.vbs /upk
slmgr /ipk NPPR9-FWDCX-D2C8J-H872K-2YT43
slmgr /skms kms.03k.org
slmgr /ato
slmgr /skms zhang.yt

Remove "This build of Windows will expire soon"

Navigate to C:\Windows\System32. Find the file LicensingUI.exe.
Take ownership, grant permissions and delete the file.

Enable offline charging

Offline charging (dual-boot only)

This method enables the phone to charge without booting into Windows. Only works if you shut down from Windows Phone.

Reboot to mass storage mode.
On your PC, open Command prompt as Administrator, then type:

bcdedit /store "<MainOS>:\EFIESP\EFI\Microsoft\Boot\BCD" /set {globalsettings} offmodecharging yes

Reboot phone.

This only works on Windows Phone 8.1. You can do this to workaround for Windows 10 Mobile:
Replace <MainOS>:\EFIESP\Windows\System32\Boot\mobilestartup.efi with the one from Windows Phone 8.1. You can obtain it by extracting it from the FFU (use WPinternals dump feature).

Charge threshold

This method forces the phone to charge to a specific battery percentage before it can boot.

Reboot to mass storage mode.
On your PC, open Command prompt as Administrator, then type:

bcdedit /store "<MainOS>:\EFIESP\EFI\Microsoft\Boot\BCD" /set {globalsettings} chargethreshold "<Battery%>"

Replace <Battery%> with the battery level you want it to charge before booting, does not contain the % symbol (for example: 50).
Then reboot the phone.