Originally Posted by
mh492
If it is a full-fare Y then you can just call the SEN hotline and rebook into C. I must admit that I have never done this for international flights since Z fares are more attractive anyway. But for domestic and inside Europe it works nicely and gives you extra mileage for just ~30 EUR extra payment. Not that the food or seats are actually worth it.
... this works only if the original ticket was sold by the airlines and not a travel agent. If the ticket is from a travel agent, they will refer you back to this TA to rebook it. I actually never managed to rebook it, because our corporate TA does not rebook you into business, even if the fare is lower, on flights which are too short for business according to our travel policy.