The quick way - but maybe not the best: reformat your rules on the fly until they are valid perl, and eval them (you wrote "write a new package" which you would then use, but that's just the same - the underlying inclusion mechanism is a string eval). Roughly something like this:

my %hash = (
    genre => 'Rap',
    artist => 'Mozart',
);

sub genre  () { $hash {'genre'} }
sub artist () { $hash {'artist'} }
sub album  () { $hash {'album'} }

my $file = 'some_file.mp3';

$_ = "RULE = (genre eq Rap or genre eq HipHop) and artist ne RunDMC to
+ /music/Other";

if(s/^RULE\s*=\s*//) {
    my ($cond, $target) = split /\s+to\s+/, $_;
    eval $cond and print "rename $file, $target/$file\n";
}
[download]

Of course you must make sure your rules don't look like

RULE = (genre eq Rap or genre eq HipHop) and artist ne RunDMC to `rm -
+r /music/Other`
[download]

--shmem

_($_=" "x(1<<5)."?\n".q·/)Oo.  G°\        /
                              /\_¯/(q    /
----------------------------  \__(m.====·.(_("always off the crowd"))."·
");sub _{s./.($e="'Itrs `mnsgdq Gdbj O`qkdq")=~y/"-y/#-z/;$e.e && print}