I wouldn't exchange the lenses. You would have to adjust the focus. The Triotar is one of the best three element lenses, soft fully open and very sharp stopped down. If you want a Rolleicord with Xenar, they aren't that expensive. I've had three Rolleicords with Xenar. Two of the Xenars were bad, and lacked the biting sharpness (yes they were checked and collimated). I have five Rolleicords with Triotar at the moment, and all of them are very good. Only the 3,8 Triotar on my Rolleicord I is soft.
Triotar 4,5/75mm: