Can you understand this?

Sure. :-)

$stop = "H* ";
$stop .= unpack "H*", "just another perl hacker";
$stop ^= "\cP" x length($stop);
print $stop;
[download]

That code prints the ugly string, X:0&q'%'#'$" &!&u&v'$&(&%'"" ' &%'"&s" &(&!&#&r&%'", that you used as a starting point.

In your japh, you just take that ugly string and reverse the transformations on it with something like this:

$stop ^= "\cP" x length($stop);
($t,$h) = split $stop; 
print pack $t, $h;
[download]

You muddy it by golfing that a bit and adding some little obfuscations, like using $go as your variable to complement the options on your substitution and relying on split's deprecated scalar context behavior. But the only "twist" is that you included the template for pack in the transformed string.

Good effort just the same. (++)

-sauoq
"My two cents aren't worth a dime.";