I think this is what you want

Example 1: //echo -s $reverse(r zn blfi mvd tlw olo)
Example 2: //echo -s $reverse(gsrh rh z xizkkb vcznkov)

Code:
/reverse {
  var %alpha = a;b;c;d;e;f;g;h;i;j;k;l;m;n;o;p;q;r;s;t;u;v;w;x;y;z
  var %n = 1,%m = $len($1-),%final.string,%mid,%letter
  while (%n <= %m) {
    %mid = $mid($1-,%n,1)
    if (%mid == $chr(32)) { %final.string = %final.string $+ $cr }
    elseif (%mid isletter) {
      %letter = $gettok(%alpha,$abs($calc($findtok(%alpha,%mid,1,59) - 27)),59)
      %final.string = %final.string $+ $iif(%mid isupper,$upper(%letter),%letter)
    }
    else { %final.string = %final.string $+ %mid }
    inc %n
  }
  return $replace(%final.string,$cr,$chr(32))
}