In SoA, this armor wasn't magical - you could combine it with Cloak for Protection +2. But after I installed ToB it became magical, so I can't have the Cloak +2 upgraded because I can't put it back after upgrading. Does anybody know how to make Red Dragon armor like it originaly was?

Truth be told, I downloaded the Ease-of-Use mode here at SP and used it precisely and ONLY for that purpose.

Extrakt it with SK and open it with the item editor. From there you can decide if it should be magical or not.

Or install my item mod. You can download it here at SP. It fixes that problem.