Not installed by default, but on the installation CD, is a utility called "RSView Tag Import Utility". That can be used to export tags to a CSV file.
You must start with a save done in .L5K format, and the utility is not exactly 'complete'. Rockwell doesn't seem to feel the need to actually make it work 100% of the time. In particular, it will fail on any tag that is over 40 characters (as is easily possible with nested levels of UDT's), but Rockwell released it AS IS, and refuses to update it even after many years.
There is also a more limited export under the tools menu, but I haven't used that in a while.