Wow. A lot of confusion in this thread.
To get ride of the nag, there are a couple of approaches. You can use a root editor to edit the build.prop file in \system. Change every occurrence of the text MD4 to MK3. This fools the updater into thinking you're already on MK3. Alternately, you can flash this in recovery:
Dev-Host - MOAR_nag_remove.zip - The Ultimate Free File Hosting / File Sharing Service
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There are already several options to flash a pre-roolted MK3 ROM, stock (or nearly so), and customized / optimized. Pay close attention to the details in these threads, and make sure you flash all the required related files. The MK3 ROM doesn't play well with modems other than MK3, for example. There are also de-knoxed MK3 kernels available.
These stock ROMs seem pretty stable now, but it's imperative that you read the threads and understand exactly what needs to be flashed, and what, if any, issues remain. If you want a 100% reliable phone, it's probably better to stay with 4.2.1 at the moment.
Stock, rooted ROMs:
[STOCK ROM] Stock 4.3 MK3 ROM [ROOTED/UNROOTED] - xda-developers
[ROM MK3 ROOTED] SPHL710 All In One Installer [ODEX/DEODEX] - xda-developers
MK3 modem:
[MODEM][FLASHABLE] MK3 Sprint Modem - xda-developers
MK3 (and other) kernels:
[KERNEL][4.3/4.4/TW4.1/TW4.3] dkp - d2spr - 12/21/13 - xda-developers
MOAR 7.01 (MK3 based customized ROM):
[ROM] [MOAR] [MK3] v7.0.1 / Clock Mod / INK / AOSP Lock / Plenty of Mods! [12.17.13] - xda-developers
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Not only can you root the MK3 OTA, you can install a custom recovery and alternate ROMs. What you can't do is install custom kernels over the Knox bootloader in the OTA kernal. This root procedure has worked for everyone who has commented (see post #30):
http://forums.androidcentral.com/sp...-hacks/337722-possible-method-root-4-3-a.html
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The OP was asking about 4.3 ROMs. Hyperdrive is 4.1.2