Thinking of a weird Minimegs/Tarnma AU where Minimus ends up as Tarn, and Damus ends up as the Duly Appointed Enforcer of the Tyrest Accord.
I feel like the DJD would feel a lot less religious, but also a lot less close. I also think Megatron would respect Minimus!Tarn a lot more than he respects current Tarn.
I actually think in this situation Minimus would be the one to suggest the DJD rather than Megatron.
There are many potential implications and routes here, and all I csn think about is oh god is this gonna be so much worse for traitors on the List and how Tarn (Minimus) would run the DJD. Especially if we're leaving Damus with Tyrest and putting Minimus through the meat grinder that is the decepticons.
I feel like Tarn (Minimus) would be a hell of a lot more neurotic when it comes to exact specific procedure within the DJD, every step of the torture-murder is going to be planned in advance and I bet that shit is timed to the dot too. I do feel like there'd be less of the creative methods that we see in canon, but the DJD's calling cards will be more set in stone and take less risks.
He is going to be such a fucking terror even to his own teammates isn't he?? Especially since, unlike Tarn (Damus), Tarn (Minimus) has that certain extra layer of distance to his character and upholding the decepticon Cause.
You're right that Tarn (Minimus)'s particular angle of zealotry would read less religious than Tarn (Damus)'s, and I feel like to him it's more like absolute immutable law. I can see a situation where Minimus is more actively constantly trying to seek Megatron's approval due to the preexisting insecurities written into his backstory, and if he's still going through some of the Tarn adjacent shit then it means Megatron has been actively feeling fuel to that as well. That Tarn (Minimus) has a much more firm moral compass, that moral compass just so happens to be firmly fundamentally broken.
Adding in the Dominus as an autobot spy playing decepticon Vos arc here is interestinggg too, because on one hand I feel like Tarn (Minimus) would want to outright kill an autobot spy rather than go halfway and just Domesticate one (even if by this point Domestication was still incurable/permanent). On the other hand, Dominus is literally his older twin brother he wouldn't have seen for millions of years by this point, and when they tear Dominus out of the Vos armor he'll be vividly aware of his own similar circumstance with the Tarn armor. I'm not sure really exactly how he'd go about it, but I fear there's no happy answers there :3
Now. On Damus as playing Ultra Magnus. Considering how Damus is (probably) not a loadbearer here, I consider it a very strong possibility that here Damus might've spent a large portion of the war more in his empurata frame as an autobot, and that when the time came his full on actual body is either reformatted up to look like a dead mech (the original Ultra Magnus) or he's getting straight up reframed full on spark transplanted straight into the Magnus Armor to be the new Ultra Magnus. Whichhhh. Causes new problems I bet.
(Though, I acknowledge a potentially marginally happier situation where Glitch/Damus stays Damus and is instead getting a proper reversal back to his pre-empurata frame, excluding the whole "we can't let them know Ultra Magnus actually died millennia ago" thing entirely)
I feel like Damus and Tyrest's dynamic could still be rough in fascinating ways, especially if Tyrest keeps bringing up Damus's past as a "criminal" (let's be honest the punishment was probably bullshit we saw what things were like on pre-war Cybertron) and talking about his role as Duly Appointed Enforcer of the Tyrest Accord as a penance/necessary for not just him but the species as a whole (but ESPECIALLY him) thing.
It's hard for me to exactly gauge how their dynamic would go before the tyrest arc, considering how we first meet Tyrest mid-psychosis and he acts very differently later on in LL after some repairs, but I do think Tyrest will project a lot of his guilt onto Damus here (especially after the Aequitas trials, since we know that was a nasty turning point for Tyrest)
This is getting long but oaughuu so much can go wrong with Tarn (Minimus), and Ultra Magnus (Damus)'s dynamics can get so crunchyyy if you really put the work into it
