Swapping elements in a list

I need to receive a list and then reverse two elements in the list. Not finding a good way to do it with the included SKILL functions (though I could have just missed it), I wrote my own. Here it is (as usual, sorry for the lack of formatting):

; swaps element at given index with following element in list
; parameters:
; swap_index: index of film to move [integer]
; input_list: list to be modified [list]
; returns: input_list with swapped elements [list]
procedure(swap_next(swap_index input_list)
   let((j final_list)
      setq(j 0) ; need external counter in for loop variable auto-increments

      ; run through input list and either grab the current element or swap the next two
      for(i 0 (length(input_list) - 2)
         if(j == swap_index then
            ; at the index to swap, dump next element and then current element into output list
            final_list = cons(nth((j + 1) input_list) final_list)
            final_list = cons(nth(j input_list) final_list)

            j++ ; increment counter since we grabbed two elements
         else
            ; for any other index, just copy the input list to output list
            final_list = cons(nth(j input_list) final_list)
         )

         j++
      )

      reverse(final_list) ; return reversed list since it was built "backwards"
   )
)

This works, but it's awfully complicated. Since I don't have direct access to the auto-incrementing loop variable, I created my own. It seemed more complicated to use foreach() than this, but I'm a hardware guy who likes to think he can write a bit of code. I wouldn't be surprised if there's an obvious way to do it and I'm just daft for overlooking it.

Thanks in advance for any advice.