I'm not sure exactly what your doing, but could you just use substr? I wrote a small sample below that outputs "pre XXXXXXX post" 
$string = "pre replace post";
$i = 4;
$j = 11;
$length = $j - $i;
$result = substr($string,0,$i) . "x" x $length . substr($string,$j);
print "$result\n";

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In reply to Re: another tricky one from lol by csotzing
in thread another tricky one from lol by lolly

Title:
Use:  <p> text here (a paragraph) </p>
and:  <code> code here </code>
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