I believe that in this case it is a question of tariff conditions. Namely, currently all LH tariffs have:
CHANGES
ANY TIME
CHANGES PERMITTED.
NOTE - TEXT BELOW NOT VALIDATED FOR AUTOPRICING.
SALES RESTRICTION 25AUG20 - 31DEC20
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REISSUE / REVALIDATION / EXCHANGE PERMITTED.
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REROUTING PERMITTED
I have changed one reservation twice today on the basis of the same point and have not had to pay anything extra.