Depending on how it's coded, could be easy or could be hard. Apparently even having the option to walk around with an umbrella took some coding magic. It isn't always simple to change even seemingly basic things with coding.
A lot of the trouble comes from the basic code itself. We know it's basically been twisted around and pushed to it's limit because it was quickly rebuilt from 1.0 which was different in a bunch of ways.

So yes, they could theoretically add separate face and head slots, but in reality it might be more complicated than you'd think.