The default mode for the steppers is "single coil drive", which is low (half) power (current).
unless the "torque" variable is set to "true" (dual coil drive),
which was done in case 0 of the original sketch (lifting heavy objects on a string).
The motors are not stressed in your project, so they can be left in low power mode.
As said before, the motors are individually switched off (zero current) when they have reached their destination, all done by the goPos() function.
if (newPos[i] == nowPos[i])val[i & 3] = 0; // cut coil power when there
I think I understand your requirement, and will try to upload some coding ideas for that tomorrow.
Leo..