Minetest: Node Metadata Editor

local esc = minetest.formspec_escape

local active_meta = { }

minetest.register_craftitem("k_random_tools:owner_change_stick", {
    description = "Owner Change Stick",
    inventory_image = "default_stick.png",
    on_use = function(itemstack, user, pointed_thing)
        if pointed_thing.type == "node" then
            local meta = minetest.get_meta(pointed_thing.under)
            local owner = meta:get_string("owner")
            local pl = user:get_player_name()
            active_meta[pl] = pointed_thing.under
            minetest.show_formspec(pl, "k_random_tools:owner_editor",
                "field[owner;Owner;"..esc(owner)
            )
        end
    end,
})

minetest.register_on_player_receive_fields(function(player, formname, fields)

    if formname == "k_random_tools:owner_editor" then
        local meta = minetest.get_meta(active_meta[player:get_player_name()])
        local it = meta:get_string("infotext")
        local pfx, oldowner, sfx = it:match("^(.*%(owned by )(.-)(%).*)")
        if oldowner then
            meta:set_string("infotext", pfx..fields.owner..sfx)
        end
        meta:set_string("owner", fields.owner)
    end

end)