Yes, this is fine, it is a reval (re-validation) instead of a re-issue.
If the route and booking class are the same and there are no change fees then you can reval the ticket which simply changes the flight number that the ticket is valid on. Even if the taxes have changed then this has no effect as there is no recalculation.
Sometimes (for a random reason) the system will not accept a reval and you have to re-issue and recalculate the tax but when it works ,a reval is the favourite kind of ticket change
Originally Posted by
corporate-wage-slave
If the end and start point is the same, the routing and class unchanged, and there hasn't been a change to taxes (etc) then she may well be correct. I would, however, check in at the first possible moment (which is 48 hours in the case of Cathay). So typically being moved on the same day does not need reticketing, merely revalidation. If you booked a long, long time ago and say a new tax has been introduced, or perhaps a really big exchange rate change, then it may still need re-ticketing, but there would be a natural bias not to do that if possible.