Yes, this is doable. Add the new class in classes.2da, and give it a new 3-letter code in the featstable column. Let's say you pick ZAL. Then you add new columns in feat.2da and call them zal_list, zal_granted and zal_recom. The game will automatically associate them with the new class if the codes match.
KotorTool's 2da editor won't add new columns, though, so you'll have to use something else. I think back in the day I converted 2das so they could be edited in Excel? I'm sure there's a few different solutions.
I know you learned that from me, but I was specifically talking about appearance.2da there. It depends on the 2da, some take extra columns and some don't.