We use contact lists and values in custom columns quite a bit. It would make our lives a lot easier if we could add columns to existing lists. Right now every time we have a new column and want to use rules against it, we have to download existing lists, create new ones, import the old list values for every list in use. Adding a column would save us a ton of time.

Thanks for the feedback, Jeremy! We'll consider this as a possible feature.

Yes, please add this! I happened upon this request while looking for instructions on how to do this.