gistfile1.txt

vnoremap <leader>d :call Test()<CR>

function! Test()
  "yank current visual selection to reg x
  normal! gv"xy
  "put new string value in reg y
  let @y = "       IF (DEBUG.GT.0) THEN\n" . @x . "\n       ENDIF"
  "re-select area and delete
  normal! gvd 
  "paste new string value back in
  normal! "yp 
endfunction