Cumulenes and polyynes are peculiar cases of the intricate relation between the electronic structure and electron transport properties of molecules. Although the direct relation between the frontier molecular orbital topology and the ballistic current density is not trivial, the circular direction of the ring current in cumulenes, and consequently the magnetic field, can be chemically controlled due to tunability of the frontier molecular orbital helicity. Any transport effect that depends on the orientation of the currentinduced magnetic effect (magnetoresitance and spin selectivity/filtering) can thus potentially be chemically controlled.