ive been hacking my switch since day one, still not banned, and while this is anecdotal i wanna share what ive done.
before emunand came out i did my hacking on sysnand. i kept it only to homebrew games and apps from the homebrew launcher, no nsp installs. i even played online while in cfw and im still fine so far. (i wasnt hacking the game or anything i just launched it from cfw)
i made an emunand for piracy when it came out, and ive stayed in airplane mode on my emmunand 100% of the time. I've installed nsps, homebrew, themes, etc on there and no ban.
basically, stay on emmunand in airplane mode as much as you can if you're super worried about a ban, and keep nsp installation to there. if you need to for some reason its been safe so far for me to use some homebrew on sysnand, but i wouldnt use themes/nsps on there.