question

There isn't a simple way, because you want to override the behaviour of the visual of a complex object system. It exists the possibility to switch off the standard and replace it with a user defined visual for straight conveyors. If there exists the node drawsurrogate you add items to this node in tree of the conveyor. If the node misses you can create it in the variables. The items of the drawsurrogate node can be placed, rotated, scaled and have shapes. Please look into the library tree to find objects how the structure looks like for this node. Then you copy this structure to your object and change the values. Each time you adjust your length you add or remove items in the drawsurrogate node and change the associated values. If this answer fits to the conveyor module objects, you can use workaround to switch off the visual of straight conveyor and place basic fixed resource object in your model and use the drawsurrogate node of this basic object to change the visual as described above.