Swapping the two benches is fine without changing the
runners.
But .... The standard mechanism for releasing the
runners is asymmetrical so to keep the ability to slide the reversed
seat forwards and backwards you must
either reverse the
runners as well (by removing them from the rail and putting them back in the other way round)
or by modifying the mechanism on the
seat. (there have been discussions on this. You could sift through a search like
reversing +(seat |seats) +(modification |runner |runners)
Choice depends on how often you'll want to change the
seat's orientation. First option if this is a one-off, second option if a regular thing.