$orig='aaa([\+\-]{1})bbb';
$qre="\\Q([\\+\\-]{\\E\\d\\Q})\\E";
$bre='\(\[\\\\\+\\\-\]\{\d\}\)';

$str=$orig;
$str =~ s!\Q([\+\-]{\E\d\Q})\E!!;
print "Replace against literal quoted: $str\n";

$str=$orig;
$str =~ s!\(\[\\\+\\\-\]\{\d\}\)!!;
print "Replace against literal bslashed: $str\n";

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

$str=$orig;
$str =~ s!$bre!!;
print "Replace against variable bslashed => $bre <=: $str\n";

##</code><code>##

c:\temp> D:\perl58\bin\perl.exe re.pl
 D:\perl58\bin\perl.exe re.pl
Replace against literal quoted: aaabbb
Replace against literal bslashed: aaabbb
Replace against variable quoted => \Q([\+\-]{\E\d\Q})\E <=: aaa([\+\-]{1})bbb
Replace against variable bslashed => \(\[\\\+\\-\]\{\d\}\) <=: aaabbb

c:\temp>perl re.pl
perl re.pl
Replace against literal quoted: aaabbb
Replace against literal bslashed: aaabbb
Replace against variable quoted => \Q([\+\-]{\E\d\Q})\E <=: aaa([\+\-]{1})bbb
Replace against variable bslashed => \(\[\\\+\\-\]\{\d\}\) <=: aaabbb

C:\temp\perl -v
This is perl, v5.6.1 built for MSWin32-x86-multi-thread
(with 1 registered patch, see perl -V for more detail)