It's not really a "normal 920". It's model number is RM-822 as opposed to the International RM-821, it has different 3G-bands and does not have any LTE bands. In addition it only supports HSPA as opposed to the RM-821 which has DC-HSPA+. Also, it has a different GPU, Adreno 320, while the RM-821 has Adreno 225. So as you see there are obvious hardware differences. Never tried flashing RM-821 firmware over RM-822 firmware, and I'm not saying it's absolutely not gonna work, but in my head it's very unlikely to work.
Basically, I wouldn't flash it with RM-821 firmware unless you are willing to take the risk of bricking it.