Is it possible to add new categories or links to search refinement panel that will be pulled from a custom 'Categories' SharePoint list?
EDIT: I am not using FAST Search but the question applies to FAST Search also.
It is possible to define a SharePoint column (e.g. Categories) as a managed property. You can then modify the "Filter Category Definition" of your refinement panel.
It is outlined in that blog post in a little more detail: http://www.ableblue.com/blog/archive/2009/12/09/adding-search-refinements-in-sharepoint-2010.aspx