Green rows with a tick means that Apple is still signing the firmware file, and you can downgrade from iOS 8.3 to iOS 8.2. To find out if Apple is still signing the firmware file, check this website. Apple doesn’t recommend downgrading so please proceed at your own risk.It is important to take a backup of your iOS device to iCloud or using iTunes so you can restore from the backup if something goes wrong.You will be able to downgrade as long as Apple continues to sign iOS 8.2 firmware file.
You cannot downgrade to iOS 8.1.2 or lower as Apple has stopped signing the firmware file You will be able to downgrade back only to iOS 8.2.You can only downgrade to iOS 8.2, you cannot downgrade to a version below iOS 8.2. So jailbreakers won’t be able to downgrade to iOS 8.1.2 or lower, to jailbreak your device using PP jailbreak or TaiG jailbreak. You will need to hurry up as Apple could stop signing any moment. If you’re having an issue after upgrading to iOS 8.3, and want to downgrade back to iOS 8.2 to see if it helps then you can follow the guide below. Apple released iOS 8.3 few days back, which includes number of bug fixes and security and performance improvements, in addition to features such as redesigned Emoji keyboard, CarPlay Wireless etc.