Hi! I love weird questions but I will be very clear, legal stuff is not my bag, I hate it and I'm admittedly not an expert on it unless you just want me to be a straight-up hater.
To be very clear, SA is not okay at all. If you're talking about consensual non-consent, or rape-play, that's not SA anymore than putting on a cop murder mystery play is murder or impersonating an officer.
It's pretend. It's roleplay. That's not the same thing.
And no, unless you're high up in the government or work in Medical Assistance In Dying (MAiD), generally murder is not legal even if someone agrees to it. Admittedly, this could vary depending on where you live but I'm fairly sure it doesn't vary that much.
Also, it's a really bad idea to hit someone in the kidneys. It's dangerous and even if your partner wants it, it's generally better to find safer types of play that won't put you possibly in jail or permanently disable your partner.
As for miscarriages, I don't know about the legality of it but it'd also be very risky and a generally bad idea. You could kill your partner easily and even if you don't, again, you can cause permanent damage and/or wind up in jail.
Most things, if I'm being honest, aren't a matter of "is this legal" but "you will likely permanently and/or severely injure your partner(s), if not kill them" and that's obviously something to avoid.
Being risk-aware during kink also means knowing when to step back and find something else or dive further into the roleplay aspect than the physical and that's important to keep in mind.
Also, yeah, I'd recommend not talking to cops at all and talking to them about kink even less.
Glad to answer, though I'm not sure how helpful this is. Lemme know if you have any other questions though, these were cool! <3