so apparently `mkVMOverride` wasn't quite what i was looking for to have certain options disabled in vm builds. it's actually used by `nixos/modules/virtualisation/qemu-vm.nix` to override things like the `filesystems` in your config when creating vm builds. thanks to someone replying on the nix discord, i ended up with:
for context, i was just testing with my `snapper.nix` configuration to see if i could have snapper disabled in vm builds.
i'm not sure if this or the solution i originally came with is less hacky, mine being to check if `/home` is defined in the build. this works because `qemu-vm.nix` does not have a `/home` mount either.
on the other hand, would what i originally have wanted be clean anyway? after all, the following might fall under flag-oriented programming?