For me, my high bar that I have yet to beat, was the time I pivoted the running OS (ubuntu) into RAM over SSH so I could unmount and image the boot drive without rebooting and loading a live USB (Which would have required a ticket with my provider to enable IPMI)
NixOS in a VM for a few weeks and made it how I liked, copied that VM to server to VNC in (laptop battery was suffering), kept customising until i had it nice… and then when it came to wipe my laptop for the nixos setup, I was bit scared.
But low and behold,
nixos-build switchand then it was all there, just like the VM. Fucking amazing.