What happens, when the shelf layout changes (e.g. box sizes)?

The I/O units are sticked into the ALU strips using Tesa poster strips. The strips can be easily removed afterwards. When the distance of the boxes in the shelves change, remove the network cable between the I/O units, move the units in the bar, stick them back and connect them with a cable of suitable length. You can assemble the cables by yourself using the supplied tools.