I have talked with CS on few occassions and I think in reality what are options and restrictions:
- Date change +-14 days until time of departure
- possible routing changes from origin and destination (I.e. prefer AY LH rather than non-AY)
- cancellation of itienary
BUT
- upgrade to waitlist means approving itienary
- at least BA leg are non-upgradeable to both AY+ and BAEC, excluding gate upgrade with avios
- Even BA HBO does not allow baggage for OWE, these tickets follow AY rules=baggage is ok
So, what I'm doing know is checking few scheduling topics over summer and then deciding, leaning to just move last leg for overnight...