my $digits_3_4 = qr{ \b \d{3,4} \b }xms;
my $url        = qr{ <a> ... </a>  }xms;

$text =~ s{ $url (*SKIP) (*FAIL) | ($digits_3_4) }
          {<a href="resident-info.pl?do_what=view&unit=$1"><b>$1</b></a>}xmsg;