I also have a Doofenshmirtz-adopts-Riddle AU where Riddle has a whole existential crisis because if following the rules = good, breaking them = bad, then why has he never been happier than living with his new villain dad who breaks who knows how many laws everyday? What does that say about him? Is he a bad person for being happy now? Why couldn't he been happy before? What is wrong with him?
And then Vanessa and Norm comfort him and Doofenshmirtz explains that children's happiness do not come from meeting impossible standards but that unconditional love and care from the people around him, and that if his parents failed to give him that, that's on them. And Perry has Riddle's parents investigated in the background and maybe he was petty about it. Haven't decided the outcome yet but he really was petty about it.
Side effect of being raised by Doof is that Riddle goes from extremely reserved + occasional surprise trauma story he himself doesn't seem to realize is not normal to extremely reserved + "Riddle, why do you [random mundane question]" "Ahh, you see, Cater, back when I was a little kid living with my biological parents...". So, still surprise trauma story, just now he tells them in Doofenshmirtz story telling format. It's sticky. After a while, the rest of Heartslabyul also ends up telling stories that way. Vil is a little scared of how it seems to spread.
He still is very rule following and a +A student, but sometimes visits Trey's club and ends up acting like an assistant without a second thought. It's an habit. Also, likes to spend time with Ortho because he reminds him of Norm and he misses his family a lot when he's at school (they have calls. He still misses them). Idia hears him say Ortho reminds him of his own brother minus the lack of a squirrel for heart and has to lie down a bit.