If you wanna play someone at multiple positions you should research the ratings hits. In '13 I recruited an ATH that would be my slot receiver and nickle back (he was good enough to be my #2 CB, but I wanted him to have a chance to rest on D).
I created him in main menu -> edit teams as both a WR and a CB and then placed both versions of him in both the WR and CB depth charts. I then looked at his ratings hits. It wasn't just awareness, but he also lost CAR and even CTH (which is obviously very important for both WRs and CBs).
I don't remember the #s, but he lost 50% for some ratings as a CB playing WR while only losing 25% as a WR playing CB.
IE it was something like this:
His CTH was 80.
If I made him a CB, he'd have 80 CTH as a CB. If I play this CB as a WR his CTH was only 40 as a WR.
If I made him a WR, he'd have 80 CTH as a WR. If I put this WR in the CB depth chart his CTH as a CB was 60.
There were other ratings than AWR, CTH, and CAR that were nerfed by playing him out of position (I remember one was really stupid like RBK or something else completely meaningless for a WR or CB).
Because he took the least ratings hit as a WR playing CB I made him a WR.
The other thing to remember is that he'll progress for the position you chose so this dude had his receiving skills improve and his cover skills never did. If your guy needs improvement in a certain area, then you should probably choose that position.