Deleting partitions shouldn't mess up anything, unless the partition was still in use by something else.

So if you have a disk that is just used for Nobora, deleting all the disks partitions will not mess up anything. If you have multiboot from the same disk then yes, you have to be a bit careful to not mess up whatever you want to not delete.

But as I said this is just to make extra sure. First try just installing Bazzite over Nobora, it should probably delete everything. If not, then you can delete partitions and reinstall again.

Another thing to note, it seems that immutable is the future of linux. The Fedora project roadmaps the Atomic desktop taking over the traditional Workstation. OpenSUSE also looks to be moving to it as the default in Leap 16. Being new to the ecosystem might be advantageous because you don't have the old habits.

Hopefully without adding too much confusion, using rpm-ostree to add systemwide new packages/applications is generally to be avoided, keep your main OS clean and stable (thankfully bazzite has done the heavy lifting here for you already for all the gaming stuff, codecs etc). General apps (office, media etc) are usually installed via flatpak (using kde discover or gnome software).

If / when you want to explore the deeper (CLI / obscure things without flatpaks) Linux world open a terminal and enter

distrobox-create --name fedora-mutable --image fedora:latest --home ~/fedora-mutable
distrobox enter fedora-mutable

You can now go ahead and use dnf, install whatever with no risk of breaking your main system. But wait, there's more, 'exit' out of fedora-mutable, type

distrobox-create --name arch --image archlinux:latest --home ~/arch
distrobox enter arch

You now have all the AUR (Arch User Repository) at your disposal, install practically any Linux program in existence, and use 'distrobox export' to put it in your main OS applications list. It's pretty glorious. Remember to make homes for your distroboxes so they don't pollute your main home.

You can always delete all data and install fresh, all installers support that.

When fiddling with the /etc/fstab if you want to automatically mount stuff, make extra sure to add the nofail flag next to the line, otherwise if the drive is missing your OS wont boot.

Oh, that should be no worry. You can always do a clean install of one distro over another. Just make sure in the setup that when you select your data partitions on your other drives that you don't remake the partitions (at that would delete them). You'll also have to deal with differences in config files in your home directory since there is variance between Nobara and Bazzite. You can just grab the ISO and install normally, deleting the Nobara partitions.