Well, Lufthansa would like to keep ground times to a minimum, but passenger demand and route structure doesn't always allow this. In the morning, plenty of long haul aircraft arrive between 5 and 7 o'clock, and they don't depart until 10 o'clock at the earliest. If a change needs to be done, they try doing it to an aircraft that has some other maintenance event and rests some hours anyway.
Revenue managemant people will be better suited to answer questions as to how it is decided which configuration to plan with and how long to stick to such plan until changing it. Such answers might not be coming onto a public forum because Lufthansa might want to keep it secret. I know that maintenance requirements do on occasion require an individual frame be substituted, and if the new plane has a different seat arrangement, it can get changed.
But they will also change according to demant. You might see a large C class on LH xxx on one day and a small one the next. High yield routes have a large C class almost every day.
Surprisingly, the layout on the A380 doesn't allow any changes that I know of, so the complexity might no longer be worth it.