Flight rebooking free (up to fare differential)

Lufthansa's website currently says "All our fares are rebookable free of charge - Fare differentials might apply". See also this summary
I was looking to book a flight flying out in January 2021 with a return in November 2021. Since it is not possible to book a flight that far in advance, I thought of setting the return date to be in July 2021. I will then change the return date in 2021 to November when those bookings are possible. Unfortunately, I have to book the flight now due to bureaucracy that I won't go into and I cannot book two one-way flights.
How will the airline decide what the fare differential is when I make the date change? If fares are the same price or cheaper in November compared to July (which historically is true), will I get this date change for free or will the airline find a way that ends up making me pay a lot more?
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Can you change flights free of charge?
Some airlines allow you to change your flight within 24 hours of booking for free. How should you change your flight if this is the case? The best way is to call customer service. That way, you can confirm your airline's policy and make sure you won't be charged any fees.What does free change possible fare difference mean?
"Fare difference may apply" means that if the flight you want to change to costs more than the flight you've booked, you will pay the difference between the fares. So if you book a flight now for $450 then need to change it and the new flight costs $600, you will pay $150 in fare difference.Can you rebook the same flight at a cheaper price?
Caveat: Changes within 24 hours of booking Then, you can simply rebook at the cheaper price. Airlines are required by law to allow full refunds on flight cancellations made within 24 hours of booking \u2014 as long as you booked the flight at least seven days before departure.Can you cancel flight and rebook with lower price?
Can I cancel my flight and rebook at the lower price? As happens with most air-travel questions, the answer will vary by airline and by your specific situation. Generally, however, the answer is yes\u2014with a few caveats. It's nearly impossible to snag a refund on a non-refundable ticket no matter what the situation.How to change flight ticket date ? How much does it cost to change my flight is cancelled ?
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