The XML ribbon code has both the tick and cross buttons. The visibility is controlled by this vba (and the similar code for the other button) so that only ONE shows at any time. The returnedVal sets visibilty to true or false.

myRibbon.Invalidate always checks this code and modifies the ribbon

'Callback for myToggleDEL getVisible
Sub getVisToggDEL(control As IRibbonControl, ByRef returnedVal)
Dim oshp As Shape
For Each oshp In ActivePresentation.SlideMaster.Shapes
If oshp.Tags("DRAFTMASTER") = "YES" Then
returnedVal = True
b_DELETE = True
Else
returnedVal = False
b_DELETE = False
End If
Next
End Sub
Not a beginners project though