After searching for hours, I posted the question here, and a minute later I found it - The Warrior Within (one needs to scroll down a bit)
In response to Zeiss Ikon's comment, from the description in the link above:
Karsman has a dozen different people living in his head, each the master of a different set of skills and hoping to gain mastery of Karsman’s body. [...]
But that life is soon interrupted, when a group of commandos arrive, coming from the wastelands as only off-worlders could. They’ve come to kill a woman, or so they say. At first the commandos merely threaten as they search. Unable to find what they’re looking for, they begin to ratchet up their measures, separating the men from the women, instigating violent encounters, and eventually staging a coup against the Muljaddy and his Temple.
Faced with the task of protecting his quiet town and a woman he might love from the commandos who could want to kill her, Karsman must balance between maintaining his personality and harnessing the personas whose skills he desperately needs.