[Galaxy Note II Android Development] miminepho:
You asked for it, there it is! The tutorial isn't too complex, but it can take some time. Make sure to have an hour, depending on the amount of data to back up.

Modified version of Tilak's tutorial for multiROM, to make AICP 11.0 and 12.1 work together. Original version : https://plus.google.com/108321221872633034471/posts/XmthQRP7jMX

What we’re about to do :

Tilak’s method didn’t work for me. The recovery wouldn’t install AICP 12.0 and would show an error. You can try his first. If it works, make sure to tell me so I can mention it here.

I found a workaround which is explained in this tutorial. The trick is to install AICP 12.1 as the primary system and then move it to secondaries with the TWRP multiROM recovery. You will not loose any data, thanks to a nandroid backup.

Please check that you have enough space on your phone or SD card to store a full nandroid backup and the required files. Also, make sure to charge up your phone.

Assuming you're running AICP 11.0 with the latest version of the official TWRP recovery for Note 2.

Prequisites :

-Download the latest TWRP multiROM custom recovery, the multiROM zip and the multiROM uninstaller zip from here https://www.androidfilehost.com/?w=files&flid=125030 (link in Tilak’s original post) and place the files on your phone or SD card.

-Download the latest AICP 12.0 nightly and place the files on your phone or SD card.

Ready ? Let’s go !

-Boot into TWRP

-Make a full nandroid backup of your current AICP 11.0 system

-Wipe Data, Cache, Dalvik Cache and System

-According to Trafalgar Square : Flash ROM & GApps (the latest nightly release of AICP 12.1)

-Boot

-Reboot to Recovery

-Flash Boot.img via TWRP (on the boot partition of course)

-Reboot

-Have fun (not yet)

-Instead of having fun : reboot into recovery

-According to Tilak : Flash the TWRP multiROM recovery zip

-Then flash the multiROM zip

-Reboot without wiping Cache and Dalvik Cache

The multiROM boot screen should show up. It’s where you’ll be able to select the system you want to boot on.

-Reboot into recovery. The recovery should now be the TWRP multiROM one that you just flashed.

-Go to the multiROM by clicking the hamburger button on the top right corner of the screen

-Go to Swap ROMs

-Select Move primary ROM to secondaries. You can change the new ROM’s name if you want to.

-Go back to the main menu and restore your AICP 11.0 backup. It will be restored as primary system.

-Now you can have fun !

Make sure to take a look at the multiROM boot screen settings in the multiROM menu in the recovery. You can disable auto boot or adjust the auto boot delay for example.

According to Trafalgar Square : Flash the Boot.img, if you update the ROM.

If you want to go back and uninstall multiROM :

Simply flash the multiROM uninstaller ZIP in the recovery. This will wipe your secondary system, that is to say AICP 12.0.

If you want to, you can flash the official img file of the TWRP recovery if you don't plan to use multiROM in the future. You can get the latest version here : https://dl.twrp.me/t03g/

Before flashing, make sure to choose the recovery partition as a destination.

If you want to update AICP 12.0

Do not use OTA. I think it won't work as SuperSU binary updates via TWRP don't (the phone reboots into recovery and doesn't start the installation process).

Simply download the latest release of AICP 12.0, place it in your phone or SD card and flash it through the multiROM menu in TWRP, in the listROMs options.

I haven't tried this yet, but it's likely to work.

Hope this helps!