Irrespective of what DL should or shouldn't allow, I was more interested in where their policy regarding involuntary changes is explicitly (technically) spelled out. Not sure it's in the CoC, haven't looked. But as others have alluded to, it may not matter so much in practice, as DL is generally good about granting waivers.

Personally, I don't think that "accepting" a schedule change that DL made should lock you into anything. I view that differently from proposing one alternative, having the ticket changed, and then proposing another alternative.