Add editable custom field to end-user view

Hi, I would like this feature too. 
Customer (End user) would want to change severity (ticket field) of the ticket when ticket is already created. For e.g. the ticket is first created with Severity "Low". Then, a few days later, they want to increase the Severity to "High". Currently, only Agent have control over this. Kindly advise. Thank you

I would like this feature as well. 

I have a use for this feature also.  I have several fields on a form that the end-user may not know when submitting their ticket but will obtain later.   I would like them to update their own ticket rather than submitting a comment with the info, and then having an agent update the fields.