At the moment, you can change the bandlength by a slider.
How about an additional button to automatically apply it's length to the distance of the parts which are connected with the band?
This would help preserving the distance of some puzzle parts when doing some actions like rebuild or wiggle.

Moreover, how about the possibility to enter the length value by keyboard?

And when will we have the opportunity to set band lengths bigger than 20?

regards,
Alex