Everything of your workflow changes can be done in trac.ini. Use TracIniAdminPanelPlugin to do that via web interface in case you only have remote access.
install AdvancedTicketWorkflowPlugin. Have
advancedworkflow.* = enabled
in your[components]
section of trac.ini.Have
workflow = ConfigurableTicketWorkflow,TicketWorkflowOpOwnerReporter
in your[ticket]
section of trac.ini.Define your own workflow in a new trac.ini section
[ticket-workflow]
. The wiki page of AdvancedTicketWorkflowPlugin will explain that in detail.