How to Edit Civ III rules
To edit the default Civ III rules, you must first go to the Tools menu and check "Custom Rules". The "edit" box on the toolbar, as well as the "Edit Rules" selection on the Rules menu should now be enabled.
Simply select the rules page you wish to modify on the toolbar, and click "edit" to begin editing rules. Make sure you save your changes to a BIC file before exiting the editor, or your changes will be lost.