Many of the parameters set on the Administration > Defaults > Configuration page can be set differently for each academic session, including the global banners (
tmtbl.global.info for a blue message at the top of the page, tmtbl.global.warn for a yellow message, and tmtbl.global.error for a red message), or the custom stylesheet (tmtbl.custom.css -- try to set it to styles/test.css which is an example used in
help.unitime.org/customizations). When editing a setting, uncheck the All Sessions toggle and select only the academic session(s) for which you want the setting. The setting will get rolled forward with the Session Configuration (step two on the Roll Forward Session page).