We have dates all over the site that need to be formatted. Instead of going to each date and formatting it with the convertDateTime tag, is there a way I can just globally change the format of how it displays dates? If they change their mind on formatting and I would be stuck going through the entire site changing every one of them.
That's about as good as it gets. You can keep the conversion pattern in a session bean if you want to be able to customize it on a per-person basis, but the same tactic applies.
The timezone for JSF conversion unless overridden is GMT and cannot be overriden globally. The formatting pattern employed is the default locale pattern for the JVM that runs the webapp (I think). So the only way to achieve specific zones and formats is on a per-use basis.