[Verizon Galaxy Note 4 General] shadeau:
I have looked around and haven't seen anyone mention this so I thought I would post about it since I've been using it and thought it was cool. I hope others find this useful.

The thread I'm talking about: http://xdaforums.com/note-4/general/dual-boot-n910f-snap-dragon-variant-t3065211

The original thread quoted by [MENTION=5132493]aukhan[/MENTION]: http://xdaforums.com/showthread.php?t=2447534

All credit goes to the original developers for this tool.

Thanks to [MENTION=5132493]aukhan[/MENTION], [MENTION=3145598]rlorange[/MENTION], [MENTION=427477]chenxi[/MENTION]along, and other contributors.

Download the first .apk (Dual Boot Patcher). That is the only app that you should need to complete the process. A video guide is posted by [MENTION=5132493]aukhan[/MENTION] here: https://www.youtube.com/watch?v=h_i3GW_s-VE&spfreload=10

That is the best walkthrough I've seen.

Since it was requested, I've made a video walkthrough of this process: https://youtu.be/5VzYED1hhUA

Basically you patch all of the .zip files that you would have flashed normally and then you flash them to a new ROM slot. If there are more questions that the video doesn't answer I'll be happy to answer them or post a better walkthrough if needed.

It should be noted that to switch back and forth you'll need to install the Dual Boot Patcher apk on both ROMs. This does not affect TWRP Recovery.

I have run this with JasmineROM as the primary and CM13 as the secondary as well as CM13 as primary and JasmineROM as Secondary. I currently have this set-up to try different ROMs without needing to completely wipe my phone and deal with backups/restores. I also use it to use CM13 as my primary while having stock options (S-Pen, Car BT, and other Samsung stuff) available in a quick reboot.

Edit:

More Specific Instructions:

1) Download all .zip files that you would flash if you were going to flash the ROM normally (ex. CM13, Gapps, SuperSu, XPosed, datafixes, kernels, etc)

2) Download the Dual Boot Patcher apk: https://snapshots.noobdev.io/ and install it on your phone

3) Open ES File Explorer or another Root Explorer app and navigate to /sdcard/MultiBoot

4) Create a folder labeled "dual" in that directory (now there is a folder /sdcard/MultiBoot/dual)

5) Open Dual Boot Patcher app and tap the three lines in the upper left then select "Patch Zip File"

6) Tap the plus button and find each of the .zip files that you will be flashing. After selecting one make sure to change "Partition Configuration" to "Secondary"

7) A file browser will now open. Navigate to /sdcard/MultiBoot/dual and save the patched zip file there.

8) You may now repeat steps 6 and 7 to add the rest of the zip files

9) Tap the check mark in the upper right to "Patch" all of the .zip files

10) Tap the three lines in the upper left again and select ROMs

11) Tap the phone icon in the lower right and push okay

12) Tap the plus button in the lower right and navigate to the /sdcard/MultiBoot/dual folder. Select the main ROM (CM13, Kyubi, JasmineROM, etc) and tap "keep location"

13) Repeat step 12 until all zips are added in the order you want them flashed (the order is important). If you mess up swipe the one that's wrong to the right to remove it from the list

14) Tap the check mark in the upper right. A console should appear and it should virtually flash the ROM as you would expect in TWRP

15) Once it says "x/x completed" in cyan text and it has stopped you can just tap the back arrow in the upper left

16) If you go back to the ROMs page there should now be a "Secondary" ROM. To test it out you'll need to select it and then reboot the phone.

17) Once it has booted and you are past the setup you'll need to enable "unknown sources" in the menu and install Dual Boot Patcher. Once it's installed, open it. It should find the two ROMs and you'll be able to select Primary from the ROMs menu and reboot back

Edit 2:

This process can be done using any of the partition configurations listed when patching a Zip file. Secondary and Multi Slots go to the System partition, data slot goes to internal storage, and Extsd slot goes to the External SD card. I recommend not using the Multi Slots since more than two ROMs is a lot on the system partition.

If you have problems make sure to set the kernel and update the ramdisk before flashing and that the files are in the right folder typed exactly as it says in the prompt when patching the file.

I have noticed many problems when using a non-Touchwiz ROM as stock and trying to dual boot to a Touchwiz ROM. I have had bootloop situations when trying to dual boot to Kyubi or PaulPizz from CM13, but with PaulPizz as primary I have no issues switching back and forth.

In the event of a bootloop you can recover your primary ROM by entering TWRP, tapping install, selecting image in the bottom right corner, navigating to the /sdcard/MultiBoot/primary folder, and selecting the "boot.img" file. This will return your phone back to the primary ROM.

Edit 3: Video Tutorial: https://youtu.be/5VzYED1hhUA

If it is too blurry I can make another one, but I think you can see what you need to just fine. I hope it helps. I also forgot to mention that if you later want to flash anything to the ROM that you're "dual booting" into then all you have to do is patch the zip files and flash them like before except you're flashing to a slot that already has a ROM now.

Edit 4: I have now tested this on Marshmallow with success. I still recommend using a Touchwiz ROM as primary and you'll need to have a kernel that's permissive. I'm using Emotion, but I think Oscar's kernel should work as well. I have PaulPizzRom.VRU2CPF3.r-2 installed as primary with the CPF3 modem and Emotion kernel and CM13 as secondary (pretty much my daily driver at this point). Everything has been working so far.