Try this - it does nothing to some of the CC types such as Repeating CCs
Code:
Sub ResetCCs()
Dim aCC As ContentControl
For Each aCC In ActiveDocument.ContentControls
Select Case aCC.Type
Case wdContentControlComboBox, wdContentControlDate, wdContentControlRichText, wdContentControlText
aCC.Range.Text = ""
Case wdContentControlDropdownList
aCC.Type = wdContentControlText
aCC.Range.Text = ""
aCC.Type = wdContentControlDropdownList
End Select
Next aCC
End Sub