We explore here the use of field evaporation in a transmission electron microscope for controlled apex modification, opening, and shortening of various types of individual nanotubes and nanowires. The technique works well for conducting carbon nanotubes but also for large bandgap silicon carbide nanowires and insulating boron nitride nanotubes. Since the length reduction does not affect the diameter of the object, we can thus compare mechanical properties at a given diameter for different lengths or, conversely, precisely tune the mechanical resonance frequencies. Opening the nanotubes also creates perspectives for their use as nano-capillaries.