challenging

Hi, All:

I have a Form Combo Box which has 5 options. The default option is
either Option1, Option2 or Option 5.

If the user switches between those 3 options, we do NOT need to do
anything. However, if the user wants to
switch from the default option (1, 2 or 5) to EITHER Option 3 OR
Option4, I will need a warning message "This is for decoration ONLY.
Please DO NOT attempt to select this. Thanks,". Then the user will
click "Ok" and
the option stays as the previous one.

Please advise!

Thanks,