Create an alias for a query var

query-var-alias.php

<?php

/**
 * Class Query_Var_Alias
 */
class Query_Var_Alias {

	/**
	 * Query var being aliased
	 *
	 * @var string
	 */
	protected $_query_var;

	/**
	 * Aliased name for query var
	 *
	 * @var string
	 */
	protected $_alias;

	/**
	 * Setup logic for query var aliasing
	 *
	 * @param string $query_var
	 * @param string $alias
	 */
	public function __construct( $query_var, $alias ) {
		$this->_query_var = $query_var;
		$this->_alias = $alias;
		add_action( 'parse_request', array( $this, 'parse_request' ) );
		add_filter( 'query_vars', array( $this, 'query_vars' ) );
	}

	/**
	 * Add our alias to the list of query vars
	 *
	 * @param string $query_vars
	 * @return array
	 */
	public function query_vars( $query_vars ) {
		$query_vars[] = $this->_alias;
		return $query_vars;
	}

	/**
	 * Replace our aliased query var with the actual query var
	 *
	 * @param WP $wp
	 */
	public function parse_request( $wp ) {
		if ( isset( $wp->query_vars[$this->_alias] ) ) {
			$wp->query_vars[$this->_query_var] = $wp->query_vars[$this->_alias];
			unset( $wp->query_vars[$this->_alias] );
		}
	}

}