If you were to use a nulled script of vbulletin but decided to buy the license, is there anyway you can transfer the forum posts, members, etc?
Why would you *want* to? You really trust someone who nulled something not to add something sneaky like a backdoor into your site? lol
No 'transfer' needed when you buy your forum a license, just submit your site with the license and replace files. But why don't start your forum licensed from the begin?
After the license has been purchased, download the licensed version and overwrite all the files. You would then maybe want to replace all mods with the official ones from vBulletin.org - they may have been modified when downloaded. I also suggest you backup the database, and ask everyone to change their passwords. You never know what has been added to the nulled versions...