I tried to replace, "Event" with "event" in the keyword metadata using the Edit>Find and Replace and checked the box, Case sensitive search, but only received an error message.
So I used the Find function and found all files with the "Event" keyword. Then changed the view in the contact sheet to "Selected" and used the Find and Replace function. This time all 55 instances of Event were replaced with "event".
Is there something I am doing wrong? or don't understand about Find and Replace?