You would have to go into either the Civ3x file or civ3xedit file under the program files-->Infogames Interactive-->Civ3-->Civ3PTW folder.
Civ3x is the main mod.bic file that changes rules for every game (default rules) so don't touch that file unless you really know what you are doing because if you screw something up, causing the game to crash, and can't figure out how to change it back you'll have to re-install the whole game! (save a copy of that file before making changes, for emergency/safety back-up).
Civ3xedit you can do the same thing, but it creates a scenario, so when you play PTW, you would just load up that scenario, then randomize the map to play by those rules (and civ names) and this won't affect the normal default rules.
When loading up either file, go to 'Scenarios' and check 'custom rules', then you can go to the 'Rules' and change the name under the 'civilazations' tab.