[vba]

Dim StartLine As Long

With ActiveWorkbook.VBProject.VBComponents("Sheet1").CodeModule
StartLine = .CreateEventProc("Click", "CommandButton1") + 1
.InsertLines StartLine, _
"Dim ans" & vbCrLf & _
" ans = Msgbox( ""All OK"",vbYesNo)" & vbCrLf & _
" If ans = vbNo Then Cancel = True"
End With
[/vba]