Prefix in New Thread - How can I do this?

[James Birkett]

This seems unnecessary as you could just ask them to put a URL extension (.com, .org etc).
To add more than 1 prefix to the set:
Prefix set ID: to make sure the set is unique. Can hold any value (click ? for help)
Title: URL extension (or something?)
Display order: Self-explanatory, click ? for help.
Use prefix set in these forums: Select the forum you want (hold ctrl and click if you want more than 1 forum).
Once you've done that, go to Thread Prefix Manager, then click 'Add Prefix' (on the right).
Fill in the fields, for help click the ?.
Be sure to make sure your related forum is set to 'Require threads to have a prefix' for this to be 100% effective.
As for SEO friendly, I'm not sure.