Because the emphasis is on the word being proclaimed, the promise binding itself to the elements, you do not have to repeat it word for word. If you did we might all be concerned over translations and "hybrids" of the four biblical accounts of the WoI.
There are subtle differences in the various accounts. Luke Jesus offers the cup twice, Matthew is the only one that says "for the forgiveness of sin" as two examples.
While it may be ok to paraphrase or not necessary to speak them verbatim, I would wonder why anyone would, and it still should be done with care and thought and never to "jazz up" communion. It does not need to be word for word, but the promise does need to be clearly presented. The desire to add/take away is a common part I think of our human condition, and not something I would ever want to see done.
Pax