Well I found it... looks a bit complicated eh? :P
Code:
alias replacemoo {
  var %tmp, %test = $regsub(%hangman.answer3,/[1-9a-zA-Z]/gi,-,%tmp)
  var %hangman.answer2 = %tmp
  var %a = 1
  var %b = $pos(%hangman.answer3,$1,0)
  while (%a <= %b) {
    var %firstpart = $mid(%hangman.answer2,0,$calc($pos($2-,$1,%a) - 1))
    if (%firstpart isnum) { var %firstpart = "" }
    var %lastpart = $mid(%hangman.answer2,$calc($pos($2-,$1,%a) + 1),$mid(%hangman.answer2,$calc($pos($2-,$1,%a) + 1),0))
    if (%lastpart isnum) { var %lastpart = "" }
    var %hangman.answer2 = %firstpart $+ $1 $+ %lastpart
    inc %a
  }
  return %hangman.answer2
}


but There's a simple mistake... can you help now?

//echo -a $replacemoo(h,hi hthere) = h-h--h--
the space doesn't appear