c:\@Work\Perl>perl -wMstrict -le
"use 5.010;
 ;;
 my $s = qq{Please;, read these&\x23xB0;, before you post 180;, if not absolutely &\x23x2013;, sure.};
 print qq{'$s'};
 ;;
 my $entity = qr{ & [\x23] x [[:xdigit:]]+ ; }xms;
 ;;
 $s =~ s{ (?: $entity , (*SKIP) (*FAIL))?  ; \K , }{}xmsg;
 print qq{'$s'};
"
'Please;, read these°, before you post 180;, if not absolutely –, sure.'
'Please; read these°, before you post 180; if not absolutely –, sure.'