Have to say from my perspective as an OC that's worked for a couple of airlines that specialise in last minute subs, I prefer to CHG the RPL that's already in there. It avoids slot delays, you know the route works and all you have to do is put in your operater code.
Even if the a/c type/route/level are different this can all be done using the CHG message, generally without affecting the slot, (granted not always true as route/level changes can bring about a slot - but it's still better to CHG than re-file surely?)
