Segmented mirrors are commonly used to construct large-aperture telescopes. We present a methodology for structural analysis and experimental results of an adjustment of a mm- to far-IR range (10 mm to 70  μm) segmented mirror panel to correct its deviation from an optimum paraboloid of rotation. The panel is made of high-modulus carbon fiber–reinforced plastic and has a shape of a 15-deg sector with a 1207  ×  390  mm² reflecting surface area. A system of mechanically operated adjusters for correcting large-scale surface deformations is described. We used our original method to correct fabrication errors and improved the surface shape accuracy from 23.8 to 4.5  μm (RMS values). The method is based on distance-to-target-surface minimization using vector influence functions and arbitrary movements. The results of the long-term panel shape stability monitoring and the effect of cooling the panel down to 77 K are also presented.