Don't quote me on this since I haven't done it, but IIRC that's something that you can only do during a fresh install

i actually don't even use microg, there's no problem at all. you don't get push messages, and some apps might not run tho i havent encountered any yet. (i don't run banking, drm, anything like that)

Yeah. I've been using it for years.

GrapheneOS prefers using sandboxed Google Play instead for security and functionality reasons, but they are pretty obscure. In theory, microG could be used to install a malicious app with elevated permissions, since it has the ability to bypass security checks. If you trust the apps you install, then it's a non-issue. It's potentially less functional as an open-source implementation, since it is not a perfect 1 to 1 replacement of Google services. You may find that there are certain functions it just can't do. I don't know of any specific examples.

The only app I've ever had trouble with on Graphene with no GS in main profile is the myq garage door app oddly.

Everything else has been fine

If I need something that requires play services I can run it in the private space

Absolutely. It was bought and installed by the previous owner. It drives me absolutely insane that this is the one app that decides to reject Graphene when everything else including banking and travel apps are running fine. MyQ blames it on CloudFlare

I don't think you can do that. But if you can, go ahead, it's not unsafe in the sense that your phone will catch fire or anything.

But you should always have backups of anything you can't afford to lose.

Yeah go for it