yes each persons system is comprised in what ever ways that persons mind needed in order to survive. that means for some people they may have one or more alters in the system who's job, purpose, reasons for being is to learn and grow in order to appear to be normal and not draw attention to the secrets and such,

that said there is set diagnostic criteria here in america for what is a dissociative type alter, how much control they have, what they can do. you can read the actual wording in my link at the bottom of my post. but the short version of all that long winded psychological wording in my link is that each alter has their own sense of agency, sense of self, their own affect, behavior, consciousness, memory, cognition, and sometimes sensory motor functioning that causes discontinuity for the one in which they reside.

example even though Rainy may have been able to learn to be happy sometimes she was still who she was...the embodiment of my sadness, sad memories, everything about her was depression crying and suicidal, she held my sad\depressed memories and traumas related to sad\depressive events. why because thats what her job, purpose and reason for being created was.