Owners of the Verizon Galaxy Note 4 have been stuck with an unlockable bootloader since the device came out more than a year ago, but that's changing thanks to noted modder Beaups. With a few ADB commands, you can unlock the bootloader and open up a whole world of modding possibilities. Of course, you might also break everything. So, proceed at your own risk.
The unlock exploit will basically change the CID of your retail Note 4 to a Samsung developer CID. You'll need several things for this including a microSD card (which will be formatted), working ADB, and a rooted Note 4. There are full instructions available on XDA, but the gist is that you push a file to the device, run it as root, and reboot a few times.
Having an unlocked bootloader means you can flash anything to the phone, like a custom recovery for installing ROMs. You could also brick the phone if you're not careful. You know what they say, with great power comes great responsibility.