The reciprocity between form and force diagrams in 2D graphic statics makes it possible to manipulate the form diagram while directly evaluating the redistribution of the forces within the force diagram. Conversely, after modifying the force diagram, the consequent transformation of the form diagram can be assessed at once. In the case of vector-based 3D graphic statics, the reciprocity between the diagrams is generally not achieved. This paper describes a series of transformations that can be applied to a vector-based 3D force diagram while allowing the corresponding 3D form diagram to adjust accordingly. Two categories of manipulations of the force diagram are described: global transformations that affect simultaneously all the elements of the diagram and local transformations, which permit the manipulation of individual elements of the diagram. Thanks to these transformations, the adjustment of the magnitude and the direction of the forces in vector-based 3D force diagrams can be used as an active operation in the structural design process.