If you want to use it to flash other C6506 variants (e.g. Canada, Mexico, etc...), you should be able to flash everything except the baseband and that will maintain your original baseband. Alternatively, you can flash the original baseband afterwards if the included baseband doesn't support your carrier. Just make sure you have a stock FTF of your firmware before you decide to go this route.
I was also able to successfully root it via DoomLord's latest thread. It will require the kernel from the previous C6505 10.3.A.0.423 stock firmware (C6506 ONLY). Customization doesn't matter, as long as it's for the C6506 and Android 4.2.2 so the kernels match. If not, you'll get into a bootloop.
Upon successful initial boot, it will ask you to download Data/MMS settings. Just as well, it will default to WCDMA connection type, so just go under Settings>Networks(more)>Mobile Networks>Network Mode and select LTE.
It is always HIGHLY ADVISABLE that you keep a stock FTF of your firmware before flashing any other stock FTF that changes your customization, so you can easily go back to your original customization or repair the phone in case something goes wrong. You can learn more about this here.
File 1: http://d-h.st/FSs
File 2: http://d-h.st/lsJ
You'll need 7-Zip or any extractor that can handle 7Z formats.