The only thing you can do in the future, is to not list
yourself as a recipient of the meeting notice.  That way
you won't "accept" it and have it post to your calendar
and it will always leave you able to update the meeting
notice.  To fix this one, you may have to send everyone a
cancellation notice to delete the original item off the
calendar then resend the updated one, without yourself as
a recipient.  Kind of messy, but worth it if it really
needs to be done!