Well good news folks, because you can apparently "re-purchase" your Days of Iron armor from the rewards book packages as many times as you like!
The perks rolls seem to be permanently locked for EVERYONE, (Titan arms are farther grenades and handcannon loader, for example), but the STATS (Int/Dis/Str) are random each time.
Got a Tier 11 build you really like? Don't wanna bother figuring out which armor pieces need to have what stats? Well just trying again and eventually you'll get the armor you desire!
NOTE: After the first reward drop, all subsequent drops will be light level 3. Breaking the armor down gives you nothing. The Ghost shell doesn't seem to do this, my tests have been Int/Dis every single time.
You fine folks may have already known this, but hopefully this will help somebody out!
Eyes up, Guardians.