Compatibility tested with: xF 1.1.4+ and xF 1.2 RC1.
Use this add-on if you like to distinguish through separate usergroups between users who were temporarily banned from those who were permanently banned.
Install this add-on. Create a new usergroup for your temporary banned users. Style this usergroup to your liking. Then, under Options->User Discouragement and Discipline, choose your temporary banned usergroup as shown in the screenshot below.