Actually, you can take OTAs on 0x1 phones.
I have experience with my dads S5, my old S6, my cousins S6 and my I9505 S4.
All of them were 0x1 KNOX, the S5 took the OTA from 5.0 to 6.0.1, the S6 took an OTA from 5.1.1 to 5.1.1 with security patch and then 5.1.1 to 6.0.1, and my S4 took a baseband update OTA from 5.0.1 to 5.0.1, but my point is, 0x1 doesn't mean no OTAs.
Provided you are not on a custom kernel and recovery, and are completely bone stock, OTAs are very much possible.
Getting back to stock simply involves flashing the entire stock ROM, doing a /data wipe and using your phone as you normally would.