Customizing Options for Closing Opportunities Records in Microsoft Dynamics CRM 4.0.

Status (statecode) is a read-only field.  It isn't a picklist, so it cannot be changed OOTB.
The option selected coordinates with the Status Reason (statuscode), and you can add additional Staude Reason to that attribute.

You'll need to Customize Opportunity and the StatusCode attribute.
Pick the Status that you want to add values to (Open, Won, or Lost) and then you can add to each picklist.

Save and Publish

Excellent. Is there any way via the CRM 4.0 SDK or other means to edit the statecode to have additional options aside from won/lost (i.e. "On Hold" or "Under Management Review")? Or to use the SDK to add additional fields to the close opportunity dialog box?

Understand that the StateCode is basically available when you are "Closing" an opportunity.

You could add another field that is for openStatus and make those picklist values available.  You could at least use Advanced Find on them at that point.  You could get really crazy and change the default views to add a flag so that you could eliminate those from most views....

There is no DeActivate or Disable for an Opportunity.

And adding a field such as openStatus something done through the SDK or through the CRM system itself? I don't see any way to edit the Opportunity Close dialog box options within CRM itself.

I suppose my only remaining follow-up question is that is it at all possible to add, change, or otherwise customize anything on the Opportunity Close dialog box, aside from the Status Reason values?