Would be a real shame if this also nuked your safetynet trust score if they realize too many people are using this escape hatch...
I really hope this ends up being possible! Play Protect seems to jump up every so often and try to scare me into turning it on. Very annoying. I've wanted to disable Play Protect permanently, but never did the query to learn how, so thank you.
What does this break?
There shouldn't be any side effects other than rendering Play Protect inert. No other AOSP component relies on this setting.
There could of course be side effects in the future when this restriction is rolled out, as in your device's Play Integrity status could be affected and your banking app/phone wallet might not let you perform app-based payments from that device.
I really hope this is done via Play Protect. You can also disable it temporarily in Google Play and install whatever you want.
I personally won't be doing this verification for my open-source apps. I have no interest in any kind of business relationship with anyone just to publish an .apk. If that limits those who can install it to people who disable Play Protect globally, then oh well.