Great, now I can get width and height.
I already noticed "ResetBoard" method, but the problem is, that after setting new dimensions, entire board information is lost. Of course it is possible to "refill" the board with instances from layout again using Physical Coordinates to Logical Coordinates (or your layout to board plugin), but I assume that under some circumstances it can cause glitches, e.g. if instance is being animated or something like that.
Another solution could be saving the board information somewhere and than load it after setting new dimensions.