Can a theme be customized by a user? Is it possible to make the header (as the default header where XOOPS has the flash) a box where a visitor can add their own name to the site?

Add a copy block "name your site" and then they could type in "John's Site" and have as a personal header.

I have my logo on the log-in page and want to keep that but change it when someone logs-in.

Thanks