In ArcGIS 10, is there a way to add a field to a feature class even if it currently contains data?
To do this programmatically, use IClass.AddField. (Do NOT use IFieldsEdit.AddField on an existing dataset).
In Python, using the ArcPy site package, you'd use
You cannot modify the actual field name of an existing field. I would LOVE to be able to do that, but even if they implement it, I bet it'll be similar to renaming in SQL. That is, the net effect is a renamed field, but the underlying operation is: make new field with new field name, copy contents from old field, drop old field name.