Another way to completely defeat scalar or array interpolation in regexes (as in strings) is by use of  ' (single-quote) delimiters for the  s/// substitution:

c:\@Work\Perl\monks\marek1703>perl -wMstrict -le
"my $s = '-#-$-%-&-~-_-}-{-^-0-$%&~_}{^0';
 print qq{'$s'};
 ;;
 $s =~ s' (?= [#$%&~_{}^]) '\\'xmsg;
 print qq{'$s'};
"
'-#-$-%-&-~-_-}-{-^-0-$%&~_}{^0'
'-\#-\$-\%-\&-\~-\_-\}-\{-\^-0-\$\%\&\~\_\}\{\^0'
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(This applies also to  m// and  qr// operators.) See perlop.