Short answers fot two questions:
Ad.1 Tripping KNOX warranty flag is permanent and irreversible (at least for now), but should not occur only from upgrading to newest official firmware version. I suspect you were trying to root your new KK.
Ad.2 Tripped flag it's only sign for service so there was attempt to install unofficial software. It not circimference with updating unit in future. Bear in mind so after upgrading to firmware with knox and new bootloader there is no way back - you can't downgrade your phone to versions with old type bootloader..
Samsung Galaxy Mega GT-I9205 with MegaFire MJ2 V11X
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