Thank you guys for making me try this function after 5 years.
IT WORKS ! — File/ Replace audio in Video.
(copy your video file first) make audio export and just replace it.
Some Video files make problems, but with QT H264 and 48/24 audio works nice. 5sec for 32sec file.
On all my macks from 10.6.8 to 10.9 with Nuendo 6.06 32/64.
juhu