And still my questions remain unanswered...
We don't know for sure, but probably not. Larian made a big point out of there being a price to pay. That's also visible in several companion quest outcomes, seemingly. On the slayer: no, definitely not. It's been explicitly stated that it's the "reward" of power. That is, it's what doesn't get you insta killed in some encounters because you're lonewolfing it. That doesn't mean anyone necessarily knows how many people you have to kill, though.
(Also note that the transformation happens on top of one such murder pentagram.)
https://www.gamepur.com/news/baldurs-gate-2s-slayer-form-makes-surprise-return-in-baldurs-gate-3
