Unfortunately you can't downgrade. As 4.2.2 was on the old bootloader. As I suggested boot into download mode, volume down and power button and see if there is a knox counter. If it says knox you have the new bootloader. If there is no reference to KNOX at all then you can safely install stock 4.2.2.
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Phone: OnePlus One 64GB
Rom: Mahdi Rom 2.7 | Der Kernel: Franco R15 with VomerTweaks
Tablet: Nexus 7 2013 32GB
Rom: SkimKat | Der Kernel: Stock SlimKat
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