You need to replace all instances of @$ too. Something like:

#!/usr/bin/perl
$_='0b1d35022f290d59436b612b034f531747493d676d130507651125713b1f7f';@_
+=qw/0B 25 00002 00011 02/;while($_ =~ /^(..)((?:..)+)$/){push @~,hex(
+$1);$_=$2;}@~=sort {$a <=> $b} (@~,hex $_);map{$~^=$~;$~++;map{$~*=$~
+[hex $_];}(split('',$_));print chr $~;}@_;
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Note: I did not check if $~ is a read-only variable in 5.8. This was more of an example of what all needs to be changed. YMMV.