It is possible although likely pretty difficult to implement, more so that could possibly be supplied in the forum. A very rough description would be to add extra fields to the event record to hold the last modified by name and date. Then design a plug-in to intercept any modifications and add the 'modified by' information to the event's record as the change takes place. Lastly would be to convert the date stored in the event record (which would be in Unix format) to human readable format, for viewing.
If you can't figure out how to do it yourself and it is important to you to have such functionality, you can contact me via email and I can try to quote you a price for making a custom plug-in for you.
Dan O.
www.much2.com