[jimworcs]

3.3.1. The travel data (flight date, flight number, point of departure and destination, passenger name) recorded on the Ticket are binding and may not be changed at all or, in some circumstances, only upon payment of a change of booking fee.

3.3.2. Should you wish to change any aspect of your carriage, you must contact us in advance. We would especially like to point out that while certain changes may involve increases to the flight price, others may not.

3.3.3. Should you have selected a Tariff which provides for compliance with a fixed Ticket sequence, please note: if carriage is not used on all individual legs or not used in the sequence anticipated on the Ticket with otherwise unchanged travel data, we will recalculate the fare according to your altered routing. The fare will thereby be determined which you would have had to pay for your actual routing in your price group on the day of your reservation. This fare may be higher than the fare you originally paid.
If the price group you originally booked was not available for the altered routing on the day of the booking, the cheapest available former price group for your altered routing will be taken as the basis for the recalculation.
If on the day of the booking for your altered routing, a higher fare would have been determined, we will subsequently recover the difference taking into account the fare already paid. Please note that we can make carriage dependent on whether you have paid this difference in price.

This is the relevant section from Lufthansa's Terms-(which you agreed to on purchase ) currently 261 does not address this problem, but there are proposals to revise it, which includes banning this practise. I think some countries also ban it, including Austria