The final kind of modification that can be made to a vBulletin installation is direct modification to the underlying PHP code of the forum. There is no direct access to the PHP code from within the vBulletin, so all of this has to be done using a text editor and an FTP program to upload the file.
Words of caution
Be careful when making changes to the PHP code that lies behind your vBulletin forum—it is very easy to damage or destroy your forum if you make incorrect changes. Also, if you do have problems, don't expect to receive support, as this is not covered. (You will be advised to reload the forum software or fall back to a backup to solve the problem.) So take care!
Be careful when making changes—always make a note of ...