Wow, it did work, my expiry has been extended to 31 December 2024! I actually received an offer to retain Diamond for 8 nights by the end of March, and started to book a couple of hotels. I then found this thread, and was enrolled into Ambassador (used to be Royal Ambassador, but lost the status and never joined since) and have now got the extension!

One booking is non refundable, but the other cancelled (but 10% penalty in Germany even if refundable...?). Will cancel a flight booking too though keep one trip to Munich - however this has saved me a lot of money, thank you FTers!