I've tried to play with this code:

$orig='aaa([\+\-]{1})bbb';
$res = '([\\+\\-]{';
$qres = '\\Q$res\\E';

$str=$orig;
$str =~ s!\Q$res\E!!;
print "Replace against variable quoted => $res <=: $str\n";

$str=$orig;
$str =~ s!$qres!!;
print "Replace against variable quoted => $qres <=: $str\n";
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Examining its output:

Replace against variable quoted => ([\+\-]{ <=: aaa1})bbb
Replace against variable quoted => \Q$res\E <=: aaa([\+\-]{1})bbb
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I notice that placing special metacharacters inside your variable doesn't make them 'effective'. However, when they are outside of the variable, they get 'noticed' by the regular expression parser. So, could it be the answer to your inquiry? ;-)

_____________________

$"=q;grep;;$,=q"grep";for(`find . -name ".saves*~"`){s;$/;;;/(.*-(\d+)
+-.*)$/;
$_=["ps -e -o pid | "," $2 | "," -v "," "];`@$_`?{print"+ $1"}:{print"
+- $1"}&&`rm $1`;
print$\;}
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