ahf wrote:

I guess I should have stressed clearly that I am NOT changing the usertype for ALL users. In my case it is changed when a user updates a particular field which makes re-approval (review by a moderator) necessary - hence the user gets demoted from author to registered. This is reversed at re-approval.

That's also the reason why I posted in the CB forum.

I supplied the way how I did it with a plugin in an earlier post. Happy to receive feedback to that solution.

This too can be done with a plugin. It's not recommended to edit core files as it will cause issue when upgrading or make your installation completely unstable.

Example:
[code:1]
global $_PLUGINS;
$_PLUGINS->registerFunction( 'onAfterUserRegistration', 'onAfterUserRegistration', 'getmyTab' );

class getmyTab {
function onAfterUserRegistration( $user ) {
}
}
[/code:1]

With the above example you can do a simple GET to get the post data if you wanted and run any code you want.