wcml_exchange_rates

/**
 * Add this code to the functions.php file of your theme.
 *
 * Assume: 
 * EUR = the default currency
 * USD = the second currency
 * 1.2 = the exchange rate EUR / USD  
 */
add_filter( 'wcml_exchange_rates', 'filter_exchange_rates', 10, 1 );

function filter_exchange_rates( $exchange_rates ) {
	$exchange_rates['USD'] = 1.5; // Change the rate EUR / USD to 1.5
	return $exchange_rates; 
}