Still sorta 1 line (though just keeping as two lines is probably best for clarity), but can just change your:

( ( $result = $htmlline ) =~ s/<tag marker>(.+?)</td>/$1/ ) =~ s/<br>/
+/g;
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to this to ditch the "can't substitute in a substitute" error:

( ( $result = $htmlline ) =~ s#<tag marker>(.+?)</td>#$1# ) =~ s/<br>/
+/g && $result =~ s/<br>//g;
[download]