I don't think this popup is customizable, but you could create a workaround with a dialog. Customize the onclick of the reactivate button to open a dialog. Following example shows you how to do this when resolving a case. I am sure it is possible when you
reactivate the case. Use a Dialog Process in Microsoft Dynamics CRM to replace the Case Resolution Form .
Kind Regards
Marked as answer byshiva_prasadThursday, May 21, 2015 4:58 PM