Install different recovery from CWM? I'm trying to switch from CWM recovery to TWRP, my phone is a LG Optimus 4X HD / LG P880. Using Simple Recovery Switcher, I tried to flash the TWRP image, but when I reboot into recovery, I get into the CWM recovery again. ADB fastboot told me "remote: bootloader is locked" when I tried to flash the recovery. So I figure the easiest way would be to install the recovery with CWM. Is that possible?

Thanks!
To install any custom recovery, you first must unlock the bootloader. There is an app for that at XDA which, other than the oem unlock method from fastboot, will allow you to unlock/relock several times.

Once unlocked, remaining steps are pretty easy:

installing CWM

The following works at least for "Open Euro" variants (I cannot tell for others):


Download the image from the CWM page (they have the LG Optimus 4X HD listed there)
give it a short name, for example recovery.img, and copy it to the root of your sdcard
open a terminal app (or run adb shell from your computer), and then

su
cat /mnt/sdcard/recovery.img &gt;/dev/block/mmcblk0p1
sync

power off the device and reboot into recovery to check if you succeeded.


Source: XDA

installing TWRP

TWRP images for the P880 you can e.g. find here. For original links and description, please refer to the TWRP page for the P880. According to the descriptions there:


download the image file
boot your device into fastboot/bootloader mode
run fastboot flash recovery twrp.img to install the recovery image
run fastboot reboot
while the device reboots, hold power and vol- to boot once into recovery (TWRP will then run a patch to prevent your device from reverting to its stock recovery, which according to the details there some P880 do).


Also worth knowing

acejavelin correctly pointed out in a comment on the question:


  If you have a flashable ZIP of CWM, TWRP, PhilZ, or even stock recovery, you can flash that recovery from any working custom recovery. Recovery runs completely in RAM, so you write a new one from recovery. Verified through personal use on several Nexus, Moto, and HTC devices.


I can confirm that with one exception: On most devices you cannot flash a custom recovery using the stock recovery, as the latter usually checks the signature. Exceptions exist, however.