Allow end users to update fields after ticket is created

Sometimes our end users change their mind, think of a better way to summarise their issue or request that we change the requester to the person who experienced the issue as opposed to the person who emailed/logge into Zendesk. I appreciate that some fields should really be untouchable to the end user at all times (eg. assignee, group, status, etc) but would like the ability to allow the end user access to their own fields (perhaps a flag on the ticket field? we currently have one that allows the end user to populate on logging, could we have one to allow the end user to populate on update?)