我已根据您的需要修改了早期的解决方案。

您需要更改以下行

$wpse0001_excerpt = substr( $wpse0001_excerpt, 0, strpos( $wpse0001_excerpt, \'</p>\' ) + 4 );

$wpse0001_excerpt = explode(\'</p>\', $wpse0001_excerpt, 3);

// unset the rest of the contents
if(isset($wpse0001_excerpt[3]))         unset($wpse0001_excerpt[3]);            
// append </p> to the end of last paragraph
if(isset($wpse0001_excerpt[2]))          $wpse0001_excerpt[1] .= \'</p>\';
// combine all the paragraphs with appending the ending tag.
$wpse0001_excerpt = implode(\'</p>\', $wpse0001_excerpt);

<?php

if ( ! function_exists( \'wpse0001_custom_wp_trim_excerpt\' ) ) : 

    function wpse0001_custom_wp_trim_excerpt($wpse0001_excerpt) {
    global $post;
    $raw_excerpt = $wpse0001_excerpt;
        if ( \'\' == $wpse0001_excerpt ) {

            $wpse0001_excerpt = get_the_content(\'\');
            $wpse0001_excerpt = strip_shortcodes( $wpse0001_excerpt );
            $wpse0001_excerpt = apply_filters(\'the_content\', $wpse0001_excerpt);

            $wpse0001_excerpt = explode(\'</p>\', $wpse0001_excerpt, 3);

            // unset the rest of the contents
            if(isset($wpse0001_excerpt[3]))         unset($wpse0001_excerpt[3]);            
            // append </p> to the end of last paragraph
            if(isset($wpse0001_excerpt[2]))          $wpse0001_excerpt[1] .= \'</p>\';
            // combine all the paragraphs with appending the ending tag.
            $wpse0001_excerpt = implode(\'</p>\', $wpse0001_excerpt);

            // $wpse0001_excerpt = substr( $wpse0001_excerpt, 0, strpos( $wpse0001_excerpt, \'</p>\', strpos( $wpse0001_excerpt, \'</p>\' ) + 4 ) + 4);

            $wpse0001_excerpt = str_replace(\']]>\', \']]&gt;\', $wpse0001_excerpt);

            $excerpt_end = \' <a href="\'. esc_url( get_permalink() ) . \'">\' . \'&nbsp;&raquo;&nbsp;\' . sprintf(__( \'Read more about: %s &nbsp;&raquo;\', \'pietergoosen\' ), get_the_title()) . \'</a>\'; 
            $excerpt_more = apply_filters(\'excerpt_more\', \' \' . $excerpt_end); 

            //$pos = strrpos($wpse0001_excerpt, \'</\');
            //if ($pos !== false)
            // Inside last HTML tag
            //$wpse0001_excerpt = substr_replace($wpse0001_excerpt, $excerpt_end, $pos, 0);
            //else
            // After the content
            $wpse0001_excerpt .= $excerpt_end;

            return $wpse0001_excerpt;   

        }
        return apply_filters(\'wpse0001_custom_wp_trim_excerpt\', $wpse0001_excerpt, $raw_excerpt);
    }

endif; 

remove_filter(\'get_the_excerpt\', \'wp_trim_excerpt\');
add_filter(\'get_the_excerpt\', \'wpse0001_custom_wp_trim_excerpt\');