Jujutsu is all about the perception of those involved and their perception/interpretation of the terms set up. Eg Prison Realm working on 1mins worth of data in Gojo's head & Yuji not including himself in 'everyone'..
For Sukuna, putting a Cursed Object inside someone he's fully convinced should survive it, probably doesn't constitute as harm. Neither does possession as it doesn't harm the body at all. If anything it strengthens it, with a better driver at the wheel etc. To Sukuna these are just applications of Jujutsu that he has mastered. So he is sure of their effects on Megumi.
In Angel's case I think it's the same. Sukuna knocks her out with CE, similar to how Gojo did with Yuji in their first meeting. Sukuna may even have copied it from what Gojo did then. A method to neutralise without inflicting bodily harm..
#JujutsuKaisen #JJK