Will I be able to downgrade?

I was using a CM12 ROM for my Galaxy S5 Sport (SM-G860P) but I decided to go back to the original Samsung way. I downloaded the stock TAR from here: http://forum.xda-developers.com/spri...g860p-t2951239 but when I installed it said "SW REV CHECK: [aboot]FUSED 2 > BINARY 1" or something like that. I've heard that it was because I can't downgrade from 5.1.1 to 4.4.2. Is it fine if I use a firmware from SamMobile and it will work? I will be using the OC5 firmware.

Thanks!
(sorry if it's a obvious question, new to ROMs)