Originally Posted by
malmostoso
Make sure you don't have any Miles&More number in the booking when you book with LH though, or fall for the "register now" trick. It tends to be impossible to swap for another program. Incognito mode in your browser is recommended.
actually i booked several flights on LH.com and used my SEN card number at the time of the booking to pre-select seats, then at the time of the online check-in changed to my TK number with no issues.