I am a cross platform player(Xbox primary, ps4 secondary), and was curious if they could share a shift account, and if so, will I be able to put the codes in twice, or would I automatically get the rewards on both?
I think all you have to do is log into your existing shift account and the rewards should automatically cross over
I play on Xbox and PC myself. You have to put the codes in separately.
So there’s zero issue with a shared shift? Awesome, thanks 
Indeed. The overarching account can be used for all sorts of stuff. But again, you have to input the code every time per “new” platform.
On the bright side, there aren’t a million and one codes for each system like in Borderlands 2 and TPS.