I want to be able to toggle a Tab visible/hidden on the Ribbon based upon the
contents of a cell.

I have the tab written in XML and the following call back works, but only
each time the file is closed and reopened. How can I make this more fluid so
it updates immediately without having to close and reopen the file? Is there
a way I can call the Callback below to make it run again?

Sub getVisibleCallback(control As IRibbonControl, ByRef visible As Variant)
Dim sShow As String
sShow = [A1].FormulaR1C1
If UCase(sShow) < "" Then
visible = True
Else
visible = False
End If
End Sub