Modify Ticket will do what you ask but it will also remove:
change tickets: subject, status, time worked, time left, priorities,
queue, dates, watchers, owner, and relationships to other tickets; add
comments and replies to tickets
[mailto:firstname.lastname@example.org] On Behalf Of Julian C.
Sent: Wednesday, July 13, 2005 6:35 PM
Subject: [rt-users] preventing requestors from assigning new tickets
In our environment we allow most of our users to have some rights in RT
(i.e. they don’t just have RT self serve access). Unfortunately, it
means that many of them can create tickets and assign them to people on
the responsible team (by setting “Owner” on ticket creation). I don’t
want this to happen.
Is there a right I can revoke from these users to prevent them from
doing this? I couldn’t find anything from reading the Wiki.
Be sure to check out the RT Wiki at http://wiki.bestpractical.com