Hi,
Sorry, the API does not support disabling a toolbar item.
Here is a workaround that was suggested by my colleague to a similar query.
<<<
A toolbar item cannot be disabled unfortunately, you would need to use its “AcadToolbarItem.Delete” method, that will suppress it from the toolbar, or use its “AcadToolbarItem.Macro” property and set it to an empty string.
>>>
Balaji
Developer Technical Services
Autodesk Developer Network