No major difference. Would his adopted heir avoid the same mistakes made by Commodus (namely alienating the aristocrats in favour of the masses and the army)? Can you promise the adopted heir would not have a son?
Civil wars will always occur in the Roman Empire no matter what Point of divergence you make. Even Marcus Aurelius faced a rebellion by one of his greatest generals.
Oh I realize usurpers and civil wars will always occur in the Roman Empire. And yes, preferably this person would not alienate the aristocrats.
Anyway, is Severus doing better the only way to to mitigate the crisis with a POD so late?