How can I? Kotor Tool won't let me export udef columns to 2da, and the file must be 2da, right?
Yes, KotorTool's 2DA editor won't let you add columns for some reason. I don't remember if Kristy Kistic's 2DA editor (
http://lucasforums.com/showthread.php?t=174367) handles adding columns, I'd give it a try first.
If not, and you have Excel you should be able to use tk102's Excel 2DA plugin to add a new column. Otherwise it's possible that you could use KotorTool's 2DA import/export to XML functionality for this, though I've never tried that so I don't know how well it works.
Or you can do it in a very roundabout way using TSLPatcher, setting it up to add a new column to the file. :)