Is there a way to change logout to only display First Name?

There isn't a really great way to do that simply because Joomla only stores a 'name' field instead of separate first/last name fields. It would be possible to make a minor update to only show the first few characters until the first space, but that may run into some odd results in specific cases.

If you'd like me to help you with that update and let you know the likely code change, just let me know.

Thanks,
Alex