Since JulesD. doesn’t want to tell more about the origin / the meaning of those words I did some research. « May your Mercury be more Freddie and less retrograde» (as I wrote in #11, not "may your Freddie be more Mercury") can be found e.g. on t-shirts :
Every Mercury should be Freddie! Show your love for astrology, horoscopes and Queen with this funny design!
Mercury in retrograde is said to bring bad luck:
Illusion or not, astrologers believe that during this time, it has an effect on life here on Earth, specifically within the realm of communication and technology. In astrology, Mercury governs communication, travel and learning.
For this reason, Mercury retrograde is blamed for everything from miscommunication to technological bugs, botched business deals, missed flights, a mechanical issue with your car or even a broken cellphone. (https://www.mnn.com/lifestyle/arts-culture/st...)
So it probably means: May good fortune be with you! or simply Good luck!
As for the translation I suggest: Möge dein Merkur nicht rückläufig sein sondern Queen-Songs singen...but...it still sounds a bit awkward...