I believe you can Odin just the MDC modem to unlock your device. But you cannot Odin a stock tar file to downgrade. Just the modem should work. Autoprime has an MDC modem file in his international unlock thread that should work. Others on mk2 have reported successfully downgrading just the modem. If it doesn't work it will either fail in Odin, or you will have to Odin the mk2 modem back to fix it.
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Phones & Tablets: Galaxy S4, Galaxy Note 8", Evo 4g LTE, Evo 3D, Acer Iconia A500, Samsung Galaxy Tab 2 10.1, Ipad 2, Nabi 2,
Rom: Rooted Stock Odexed, Hotspot Mod, Xposed, Wanum, several other xposed tweaks