I've come to understand that Split personalities are more than a simple "mask." It's a soul deep thing, rather than a simple act for convenience.
I see it as a state of being, a way of surviving.
Like everything, it can be positive or negative and true or false depending on how you perceive it and whether it is a personal experience or an opinion or not.
I wonder whether the OP will end up getting back to this.
I think once I understand what the OP is referring to when he/she speaks of Split personalities, then I can get to making a few suggestions of my own.