Editable for who ? The user ? Or the developer ?
If you use a Keyword field of Dialog type, you can tick a property that allows for user edition. This requires a certain programming effort to make the new choice available to other users, though.
As for parameter lists, it is simple to include in the application and allow specific users, not only developers, top modify the list of choices for given keyword lists. Another bit of programming is required.
So which of these two best corresponds to your question ?
Pascal.