[itsm] ChangeBuilder question

Hello, I'm getting the grip on otrs, albeit quite a newbie for now... I have configured two roles: "Change Managers" and "Support"; the first is member of the default group "itsm-change-manager", the second is member of "itsm-change-builder", and of course few agents associated with a role or the other. I would like to disable the change of state "Approved" and/or "Rejected" for agents belonging to the role "Support", I would like to give only to the change managers the possibility to approve/reject. Essentially my problem is that any agent with permissions to create a change, can also change its status into approved. Thanks in advance for any help :) Regards, Sono