[Galaxy S 5 Q&A, Help & Troubleshooting] Admin0389:
Solved! Try at your own risk!

Thanks very much to iNTER5Love for leading me in the right direction!

SM-G900F Only!

As of today I am rooted running a post-June 2014 ROM and my KNOX status is 0x0!

Back story: I live in the UK and I bought a grey import S5 SM-G900F to save some cash (about £150!). It came with a different language and non-UK region specific ROM. I wanted root but my phone had a post-June 2014 ROM so TowelRoot wouldn't work. Keeping KNOX 0x0 was important to me also (this is day 1 and I didn't want to lose the warranty immediately.)

Rant: That said, I refuse to accept rooting voids the warranty. Despite what Samsung say, we are European consumers and we have rights! If root did not directly damage your device and you can prove it (after 6 months) or Sammy can't prove it did (before 6 months) then you have a warranty! Be prepared to fight for it though.

To business:

In my experiments I found that you can feel free to do the following without tripping the KNOX counter:

You can flash a different region ROM as long as it's official (e.g. from SamMobile)

You can root using TowelRoot

You can unroot using SuperSU

You can flash kernels using ODIN (again, as long as they are from official Samsung ROMs)

You can mess up at least once :P I accidentally flashed a Virgin Mobile ROM instead of a carrier-free ROM. I repeated the steps again and I was fine.

Materials you will need:

Target ROM (the ROM you want to be on when we're done)

Donor ROM (a ROM identical to the target, but with a build date before June 2014)

TowelRoot (for the 0x0 KNOX-safe root) - https://towelroot.com/

tar-Tool_Odin3-v3.07 (for preparing the donor and target kernels for flashing) - http://xdaforums.com/show....php?t=2446269

ODIN 3.09 - https://mega.co.nz/#!UdRRyCAT!H4FyVxYynNWvXqRNmnpMGQRCP-dG3uykgP2pT4rh8Ek

I've put the steps I took into guide form as follows...

Download the latest version of the ROM you want (Target ROM) AND a version of the target ROM with a build date before June 2014 (Donor ROM). The ROMs MUST be official ROMs released by Samsung (e.g. from SamMobile)

Flash the target ROM. The one I picked was a UK version and I was coming from a Baltic EU ROM.

Factory reset (not essential, but good for clearing residual bloatware)

Copy TowelRoot (https://towelroot.com/) on to your device now! (I found that after the next step the system is very unstable)

Extract 'boot.img' (the kernel) from your donor ROM (using 7-zip)

Create an boot.tar.md5 from the 'boot.img' you just extracted using tar-Tool_Odin3-v3.07 (http://xdaforums.com/show....php?t=2446269)

Flash the file you just created with ODIN

Install SuperSU (or an SU manager of your choice – Essential to protect you from rogue apps!)

Run TowelRoot

Extract 'boot.img' from your target ROM

Create a boot.tar.md5 (same as before)

Flash the new boot.tar.md5

Finished :)

You are now effectively running your full Target ROM (we temporarily swapped out the kernel, then swapped it back in). Your system is now fully rooted. Your KNOX counter reads 0x0.

Closing Notes:

I've been researching for at least 6 hours. I've easily missed references, if you think I've used something of yours please PM me!

Please report back so others can benefit from your experience!

There is no guarantee this will work for you! Everything you do is at your own risk. If warranty is essential to you then don't try this.