I very nearly sold my PSM as the straps were the most annoying ever! So I played around with them and found this way to convert from crossbody to backpack without removing the straps from the bag.
(Disclaimer: this might cause wear of the leather straps quicker by doing this so be sure you’re happy with that first.)

(Disclaimer: this might cause wear of the leather straps quicker by doing this so be sure you’re happy with that first.)
