I wouldn’t recommend moving store from /nix/store as this would prevent cache usage and I think some packages incorrectly assume /nix/store is the store path.
This can be done, but considering you want to move /nix/store to another partition rather than say need multiple stores for whatever reason, you may consider mounting location on your another partition to nix store.
mount --bind /path/to/nix /nix
It’s also possible to use btrfs subvolumes or zfs datasets if you use those particular file systems.