1) Can I use C3PO's ability to resolve a "blank" as a "special?" My reading of the Rules says yes
2) Can I use C3PO to resolve a "modifier" die as if it were not a "modifier" die? This boils down to whether the "+" is part of the value, part of the die symbol, or something else entirely making that side of the die follow "modifier" rules. I think you can't use it due to the third possibility per my reading of the Rules Reference.
Thanks!