Within the framework of Lanzhou quantum molecular dynamics (LQMD) transport model, we investigate the influence of the neutron-skin thickness of neutron-rich nuclei on the pion emission in double-charge exchange reactions near the $\mathrm{\Delta }$-resonance energy. In particular, we study rapidity spectra, transverse momentum spectra, and charged pion ratios. The reactions induced by pions are associated with multiple processes of pions, nucleons, and $\mathrm{\Delta }$ resonances, correlated with the neutron-skin thickness. It is found that the kinetic energy spectra of the ${\pi }^{-}/{\pi }^{+}$ ratio are sensitive to the neutron-skin thickness of neutron-rich nuclei, used for extracting the subsaturation-density symmetry energy. The double-charge exchange reactions are influenced by the neutron-skin thickness, in-medium properties of resonances, pion-nucleon potential, and pion-nucleon scattering. Possible measurements are proposed for future experiments at the High-Intensity Heavy-Ion Accelerator Facility (HIAF) in Huizhou.

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• Charge-exchange reactions
• Meson & hyperon induced nuclear reactions
• Nuclear matter in neutron stars
• Nuclear reactions
• Nucleon distribution