WordPress 抜粋と「続きを読む」のカスタマイズ小ネタ ref: http://qiita.com/gatespace/items/61e40a5bdb30a4f80a83

excerpt-length.php

<?php
/**
 * Filter the except length to 20 characters.
 *
 * @param int $length Excerpt length.
 * @return int (Maybe) modified excerpt length.
 */
function wpdocs_custom_excerpt_length( $length ) {
    return 20;
}
add_filter( 'excerpt_length', 'wpdocs_custom_excerpt_length', 999 );

get-the-excerpt-add_link.php

<?php
/**
 * Filter the excerpt string link to the post.
 *
 * @param string $post_excerpt The post excerpt.
 * @param WP_Post $post Post object.
 * @return string (Maybe) modified "read more" excerpt string.
 */
function my_get_the_excerpt( $post_excerpt, $post ) {
    $more = sprintf( '<a class="more-link" href="%1$s">%2$s</a>',
        get_permalink( $post->ID ),
        __( 'Read More', 'textdomain' )
    );
    return $post_excerpt . $more;
}
add_filter( 'get_the_excerpt', 'my_get_the_excerpt', 10, 2 );

remove-more-link-scroll.php

<?php
function remove_more_link_scroll( $link ) {
    $link = preg_replace( '|#more-[0-9]+|', '', $link );
    return $link;
}
add_filter( 'the_content_more_link', 'remove_more_link_scroll' );

wpdocs-excerpt-more.php

<?php
/**
 * Filter the excerpt "read more" string.
 *
 * @param string $more "Read more" excerpt string.
 * @return string (Maybe) modified "read more" excerpt string.
 */
function wpdocs_excerpt_more( $more ) {
    return '...';
}
add_filter( 'excerpt_more', 'wpdocs_excerpt_more' );

wpmp-config-sample-ja.php

<?php
$wpmp_conf['excerpt_mblength'] = 10;