Raindrops　取扱説明書

add_filter( 'raindrops_wareki_gengou', 'new_gengou', 10, 4 );

function new_gengou( $wareki, $gengou, $nen, $seireki ) {

	if ( (int) $seireki> 2014 ) {
		$nen= $seireki - 2014;
		return '新元号' . $nen;
	}
	return $wareki;
}