I wanted to develop a duplicate General Settings Page instead of the built in one and all the settings on the built-in General Settings Page will also be displayed on the new General Settings Page.. the purpose of this is add some codes like inserting some options of a new table. How to accomplish this?
You don’t. You would have to keep your new page in sync with the core file each time WordPress is updated … that would not be very pragmatic.
Hook into the
register_setting() and add your code here.
There is a third parameter for
register_setting(): you can register a callback function here which used before the value is saved to the database.