I am also unable to get the "Label" column to work as the wiki describes. I am betting the explanation was based on released BioWare documentation, which in this case means this feature was not implemented.
The wiki states the Label fields is not used by the game engine, it just makes it easier to locate specific spells within the file 2da. You'll need to edit the .tlk file to change the spell name.
To make it work:
Pick a blank entry in the .tlk file, and add the new spell name.
In the spells.2da, add the line number in the .tlk file to 16777216. That is number you'll need to enter in the Name field in the spells.2da file for your spell.