The original post wondered about the requirement of "breaking in" an accordion. I have now had two new boxes, A beltuna CBA and a Baffetti TexMex DBA. I did nothing regarding the Beltuna (Out of ignorance?) but did a simple operation on the Baffetti. New accordions have rather stiff bellows which results in extra effort required to open the bellows. Rather than have the bellows "loosen up" over time (as with the Beltuna) I did the following with the Baffetti:
Close the bellows completely. Now open the bellows on the top only, keeping the bottom closed. Do this as far open as you can manage. Then with all pallets closed, switch the "top" orientation to the "Bottom" without closing the bellows. Repeat a dozen times. Then open the bellows completely, as far as you can. Then "bend" the bellows towards the aforementioned shapes (you will, of course, not be able to achieve full closure of either the top or bottom, as in the previous exercise). You will hear a crackling noise as the bellows folds give up their stiffness. Move the "cabinets" up and down, as one would with a "slinky", causing the bellows to flex over their entire length. Do this in all four directions several times or until the resistance diminishes. After that, before playing, I open the bellows as far as I can, in a straight line and allow the bellows to remain as such, holding them open, in my lap, to the max extension for 5-10 minutes. I then proceeded to play. This approach relaxed the bellows almost immediately and made the accordion feel like an old friend. I did this several years ago and have experienced zero deleterious effects since.
The other thing I did was to take the shoulder straps, before installation, bend them into a sharp 180 degree angle and then "slide" them up and down several times against themselves (one at a time), causing the leather to kink at the 180. This softened the straps up and made them more pliable and conform to my body better.
Both of these efforts were solely to accelerate the "break in" time and achieve comfort more rapidly.
I also noticed that over time, the "button press resistance" diminished, but that would require use, not some trick.
Press on...
Waldo