It's possible. Manipulation covers all kinds of good stuff I want in OS-- dysfunctional relationships, persuading, OCD, dementia, envy, etc. I could fill up that side section with gists already in the program.
I wonder if I can keep Changing One's Nature. When considering that Domain for OS, I also considered Playing a Role (since there are characters who don't want to lose roles, like the relative who doesn't want to stop being manager and I want to put some acting/performing in there, but I like Becoming better) or Developing a Plan since they would need to figure out how to save the business and fix relationships (don't characters in all stories have to plan to reach their goals? What makes this Concern special?), but when I mess around with my story form, I keep coming back to Becoming and the Responsibility quad-- not sure if I should trust the instinct or if that means I'm afraid to try something less familiar. The stuff under Developing a Plan is more abstract, less exciting to me (except for Ability vs Desire, which is a good conflict in the story).
Ideally, I'd say:
OS: Manipulation, Changing One's Nature, Responsibility, sort out Control/Uncontrolled and Temptation/Conscience later
MC: Fixed Attitude (he does have a problem with low worth), Innermost Desires, Denial, sort out Temptation/Conscience and Hinder/Help later
IC: Situation: Situation, Future, Preconception. I'm not sure how situation works here, although him being a (comparatively) normal person and being the one to find MC has influenced MC. MC relies on him. I don't know if I need something more concrete. I like Hinder/Help, Control/Uncontrolled. IC does challenge MC's Preconceptions about what will happen in the Future.
RS: Activity, Obtaining, Morality. They do a lot of stuff together and I like Morality vs. Self-Interest in their relationship. I'd thought Activity would've gone under IC for being something that IC pushes on MC because he wants to Obtain benefits from it, but I guess it involves both of them if MC flakes out due to his fears.
I also considered:
OS: Playing a Role
MC: Impulsive Responses (Worry/Confidence, Value/Worth are relevant)
IC: How Things Are Changing (he influences MC in matters of Threat/Security. He also learns that if just diving in to face a fear doesn't work, which is an incident that makes his steadfastness waver, taking small steps to expose himself to it can work and he passes that on to MC)
OS: Developing a Plan (Sense of Self and Circumstances seem relevant)
MC: Memories (he's haunted by past regret and failure)
IC: The Past (he deals in fixing up old stuff, seeing the worth in "junk," including MC. He's also affecting MC's predictions of how his life and the future may go)
RS: Understanding (Interpretation and Conditioning seem relevant)
I wonder if MC could be in Situation and IC affects his Fixed Attitude. He's in a rough situation and wants to fix it, but I figured his mental problems were worse (and one situation could possibly be resolved if not for someone else refusing to participate with good reason, but couldn't one character's internal issue be another's Situation?) so I used internal Domains. I don't know if Do-er works. I guess acting on an external compulsion and/or hiding might be Doing, but a lot of times he thinks a lot, trying to figure out what to do before acting.
Re-read the Collateral article. I could say that the OS characters are stuck in a dysfunctional rut (the caretaker and relative really need their relationship changed, but it only became a problem when her condition changed her thinking to make her paranoid), but MC's thinking is stuck. Sure, a stream of thoughts is something that needs to be halted, but those thoughts are composed of the same stuck cognitive distortions (like black and white thinking or focusing on the negative, but aren't those ways of thinking, which is Manipulation?) and beliefs.