Is there an extension available that allows you to make certain category options (on a 'pick list') non-selectable, but are still there/reportable? And can you do this based upon a previous field selection? E.g. The 'pick list' for a field called 'Group Name' doesn't allow an 'old' choice to be selected, but it is still there on other records and is reportable. And could the availability of the pick list be dependent upon a previous choice, e.g. an 'Area' field calculated using address?
With regard to the second part of your question - yes, there is my Field Lookup extension which allows you to "chain select" - much like picking a country will limit the choice of available states, you can make one select list dependent on another.
However, it's still in an early (i.e. unfinished) state; I actually have some funding to flesh it out a bit more, but it's not the priority of the client at the moment. If you open a new question around its use, I can document it enough for you to get it working (if it meets your needs without modification; it likely does).