[T-Mobile Samsung Galaxy S 5] mattlgroff:
By "Bypass" this is meant to circumvent the 2.5GB/3GB/5GB tethering limit to T-Mobile's "Unlimited Nationwide 4G" data packages, and not tested on other plans.

I A NOT RESPONSIBLE FOR ANYTHING YOU DO TO YOUR PHONE!

As some of you may have noticed, with the NF6 update there is no longer a /system/csc/ folder or any customer.xml files to modify that hard-code the APN into the device. I did my usual tinkering and managed to get the bypass up and running again.

Please note that even with this bypass, your traffic will still be seen by T-Mobile as coming from foreign devices, and if they fail their HTTP-Header check for approved types of devices then the Tethering will not work without a VPN to hide the HTTP-Headers. Interesting enough, here are devices I have found to work in my travels.

iPhone

iPad

Android Phones & Tablets

Safari on OS X. (Yes, only Safari. Chrome doesn't work without hiding traffic in some way.)

Some things I have found will NOT work without hiding traffic:

Game systems. (PS4, Xbox One, Nintendo 3DS, Nintendo WiiU)

Windows Desktops/Laptops.

Browsers other than Safari on OS X.

Some tips to avoid using a VPN (since that leads to a slow down of connection speed) is if your system supports a user-agent switcher. This will change the user-agent in the HTTP-Headers of your traffic to appear as another device. A common problem Windows users run into when using a User-Agent Switcher Extension in Chrome for example, is that they choose a mobile device to hide their usage. While this may work for most cases, if you wanted to watch Netflix or not be bothered by defaulting to the "Mobile friendly" versions of webpages, you can instead add a generic user-agent for Safari on OS X. I've done it in the past and its worked incredibly well.

Anyway, enough blah blah blah, here is how I set up my Tethering Bypass on NF6. I am not the original creator of these bypass concepts, just someone who put them together in the proper way so that its worked for me on NF6.

Also feel free to discuss a better/easier way of a Tether Bypass!

The Guide:

Tethering Bypass for the T-Mobile Samsung Galaxy S 5 NF6 software version in 10-ish steps.

This guide contains references to Paid apps from Google Play that are highly recommended and you should not report issues with this if you are using "pirated" versions of them. Support these hard-working developers!

1. Root your device with whichever method works for you if you are not already rooted. I used CF-Auto Root by Chainfire (http://xdaforums.com/showthread.php?t=2696537), but note that this does trip the Knox counter and the counter cannot currently be reset as of 7/14/2014

2. Download Root Explorer and SQLite Editor from Speed Software on Google Play.

3. Using Root Explorer, go to /data/data/com.android.providers.settings/databases/settings.db and open it (clicking on it) with SQLite Editor.

4. Choose 'system' and then hit the + sign in the top right corner to make a new value. This entry is called "tether_dun_required" (without ""), and the value will be 0.

5. Download APN Backup and Restore app from Google Play. Using Root Explorer, move this app from /data/app/com.riteshsahu.APNBackupRestore-1.apk to /system/priv-app/. Reboot the device now.

6. Open APN Backup and Restore, ignore the ICS warning. Hit the menu button in the top right and Disable ICS Check.

7. Download the GalaxyS5NF6APN.xml attached (unzip it first...), and move it to /sdcard/ApnBackupRestore. All I did was change 'pcweb.t-mobile.com' to 'fast.t-mobile.com' so you can do this on your own if you prefer.

8. Choose "Delete APNs" on APN Backup & Restore. Then choose "Restore APNs" and select the GalaxyS5NF6APN.xml or the one you created with the change.

9. Make a new APN under Settings > More networks > Mobile networks > Access Point Names with the + sign. It'll look exactly like below.

Name: T-Mobile US LTE

APN: fast.t-mobile.com

Proxy: Not set

Port: Not set

Username: Not set

Password: Not set

Server: Not set

MMSC: Not set

Multimedia message proxy: Not set

Multimedia message port: Not set

MCC: 310

MNC: 260

Authentication type: Not set

APN type: default,supl

APN protocol: IPv4

APN roaming protocol: IPv4

Turn APN on/off: APN turned on

Bearer: Unspecified

Mobile virtual network operator..: None

Mobile virtual network operator..: None

Make sure the green bubble is selected next to the one you just created.

10. Download WiFi Tether Router from Google Play. You can find setup instructions for the Samsung Galaxy S 5 on the developer's web page here: https://sites.google.com/site/wifitetherrouter/

Also, feel free to discuss/create a better/easier method. This is just what I worked up and it works for me.