First, make a backup of your current BCD with bcdedit -export backup_file.bcd
. If you have BitLocker enabled on your boot drive, it needs to be disabled until after your done changing things.
If you just want the menu to show: bcdedit /delete {bootmgr} default
Booting the computer has nothing to do with the registry, only the BCD controls the boot process.
Adding WinRE is a bit involved; is there something specific you're looking for, or you just want the whole environment?
Edit:
To install WinRE (the easy way):
- Get a copy of winre.wim and boot.sdi from your Installation CD & WinAIK. Directions here, steps 1, 2, and 5. Put boot.sdi in your \boot directory (note it might be on an unmounted partition, check Disk Manager for one). Winre.wim can go anywhere, just make it simple.
run these to add WinRE to your BCD:
Bcdedit –create {ramdiskoptions}
Bcdedit –set {ramdiskoptions} ramdisksdidevice boot
Bcdedit -set {ramdiskoptions} ramdisksdipath \boot\boot.sdi
You now have the ramdisk options in place.
Bcdedit –store c:\BCD –create /d “WinRE” /application osloader
Note the GUID it gives you as you'll need it for the next several lines:
Bcdedit –set {guid1} systemroot \Windows
Bcdedit –set {guid1} detecthal Yes
Bcdedit –set {guid1} winpe Yes
Bcdedit –set {guid1} osdevice ramdisk=X:\Path\To\WinRE.wim,{ramdiskoptions}
Bcdedit –set {guid1} device ramdisk=X:\Path\To\WinRE.wim,{ramdiskoptions}
This is almost all from memory; so it's possible I forgot something. I don't know of any easy way to make booting into WinRE a one-shot deal.