我设法通过以下方式完成了我想做的事情（ 不使用Regex ）：

• 解析字符串的每个字符
• 删除所有<a>标签（将它们复制到临时数组并在字符串上保留占位符）
• str_replace 新字符串以替换所有关键字
• 通过原始<a>标签重新填充占位符

如果有人需要，这是我使用的代码：

$str = <<<STRA
Moses supposes his toeses are roses,
but <a href="original-moses1.html">Moses</a> supposes erroneously;
for nobody's toeses are posies of roses,
as Moses supposes his toeses to be.
Ganda <span class="cenas"><a href="original-moses2.html" target="_blank">Moses</a></span>!
STRA;

$arr1 = str_split($str);

$arr_links = array();
$phrase_holder = '';
$current_a = 0;
$goto_arr_links = false;
$close_a = false;

foreach($arr1 as $k => $v)
{
    if ($close_a == true)
    {
        if ($v == '>') {
            $close_a = false;
        } 
        continue;
    }

    if ($goto_arr_links == true)
    {
        $arr_links[$current_a] .= $v;
    }

    if ($v == '<' && $arr1[$k+1] == 'a') { /* <a */
        // keep collecting every char until </a>
        $arr_links[$current_a] .= $v;
        $goto_arr_links = true;
    } elseif ($v == '<' && $arr1[$k+1] == '/' && $arr1[$k+2] == 'a' && $arr1[$k+3] == '>' ) { /* </a> */
        $arr_links[$current_a] .= "/a>";

        $goto_arr_links = false;
        $close_a = true;
        $phrase_holder .= "{%$current_a%}"; /* put a parameter holder on the phrase */
        $current_a++;
    }    
    elseif ($goto_arr_links == false) {
        $phrase_holder .= $v;
    }
}

echo "Links Array:\n";
print_r($arr_links);
echo "\n\n\nPhrase Holder:\n";
echo $phrase_holder;
echo "\n\n\n(pre) Final Phrase (with my keyword replaced):\n";
$final_phrase = str_replace("Moses", "<a href=\"novo-mega-link.php\">Moses</a>", $phrase_holder);
echo $final_phrase;
echo "\n\n\nFinal Phrase:\n";
foreach($arr_links as $k => $v)
{
    $final_phrase = str_replace("{%$k%}", $v, $final_phrase);
}
echo $final_phrase;

输出：

链接数组：

Array
(
    [0] => <a href="original-moses1.html">Moses</a>
    [1] => <a href="original-moses2.html" target="_blank">Moses</a>
)

词组：

Moses supposes his toeses are roses,
but {%0%} supposes erroneously;
for nobody's toeses are posies of roses,
as Moses supposes his toeses to be.
Ganda <span class="cenas">{%1%}</span>!

（上）最终词组（替换为我的关键字）：

<a href="novo-mega-link.php">Moses</a> supposes his toeses are roses,
but {%0%} supposes erroneously;
for nobody's toeses are posies of roses,
as <a href="novo-mega-link.php">Moses</a> supposes his toeses to be.
Ganda <span class="cenas">{%1%}</span>!

最终词组：

<a href="novo-mega-link.php">Moses</a> supposes his toeses are roses,
but <a href="original-moses1.html">Moses</a> supposes erroneously;
for nobody's toeses are posies of roses,
as <a href="novo-mega-link.php">Moses</a> supposes his toeses to be.
Ganda <span class="cenas"><a href="original-moses2.html" target="_blank">Moses</a></span>!