bbp_set_user_role( int $user_id,  $new_role = '' )

function bbp_set_user_role( $user_id = 0, $new_role = '' ) {

	// Validate user id
	$user_id = bbp_get_user_id( $user_id, false, false );
	$user    = get_userdata( $user_id );

	// User exists
	if ( !empty( $user ) ) {

		// Get users forum role
		$role = bbp_get_user_role( $user_id );

		// User already has this role so no new role is set
		if ( $new_role === $role ) {
			$new_role = false;

		// Users role is different than the new role
		} else {

			// Remove the old role
			if ( ! empty( $role ) ) {
				$user->remove_role( $role );
			}

			// Add the new role
			if ( !empty( $new_role ) ) {

				// Make sure Forums roles are added
				bbp_add_forums_roles();

				$user->add_role( $new_role );
			}
		}

	// User does don exist so return false
	} else {
		$new_role = false;
	}

	return apply_filters( 'bbp_set_user_role', $new_role, $user_id, $user );
}