my $pchr = "KQRBNP";
my $w1 = "QRKPNBNBQRK";

my $ascii = join '', map chr $_, 0..length($pchr);
my $w2 = join '', sort split //, eval "\$w1 =~ y/\Q$pchr\E/\Q$ascii\E/r";
eval "\$w2 =~ y/\Q$ascii\E/\Q$pchr\E/";

print "$w1 --[$pchr]--> $w2\n"