Manipulating POST variables received via form submit inside Serverside PHP Code
Can I manipulate the POST request inside serverside PHP code ? Yes, you can. You can set the values of $_POST like any other variable.
$_POST['name'] = 'Some new value';
It's not a good idea and it's not a best practices of programming to manipulate global variables manually. $_POST must be used to handle data that is send from browser to server.
Try to create your own global variable to manipulate your data instead of manipulate $_POST directly.