I find this the easiest way:

Open windows explorer
Traverse to the folder that holds the addin
Select the addin and rightclick on it.
Choose properties
On the Summary tab, you can change the:
Title and Comment.
(either in the simple or advanced dialog)

The title will be what you see in the listbox.  You'll see the comment at the
bottom of that dialog.

Hi Mark,

   The information displayed by the Tools > Add-Ins dialog is read from the
Excel workbook properties. Turn the IsAddIn property of your XLA to False so
you can see the workbook. In the Excel user interface choose File >
Properties from the menu to get the Properties dialog.

   On the Summary tab of the Properties dialog the Title entry is used as
the list entry for your add-in in the Add-Ins dialog list and the Comments
entry is displayed at the bottom of the Add-Ins dialog when you select the
entry for your add-in from the list.

thanks guys!