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Porous carbon is well known as a good candidate for the development of electrochemical double-layer capacitors. Predominantly, many conventional carbons are microporous and often well described by the assumption of slit pore geometry. However, there is a class of carbons that is significantly different from the others, namely templated mesoporous carbons. In this work, we study electrosorption-induced deformation in CMK-3-like mesopores having nonconvex geometry applying a mean-field approach. The model is based on the modified Poisson-Boltzmann equation taking into account the excluded volume of the ions within the hard-sphere model in the Percus-Yevick approximation. We assume that the deformation is caused by two effects: ion osmotic pressure and electrostatic interactions of the electric double layers on charged rods. The latter were calculated via the Maxwell stress tensor agreeing with the modified Poisson-Boltzmann equation. We estimated the pore-load modulus of the CMK-3-like material and found an agreement with the previously obtained values by small-angle neutron scattering (SANS). Additionally, we studied the differential capacitance in the non-convex pore geometry and found that the behavior of the differential capacitance profiles was similar to that of the profiles obtained for flat electric double layers. Namely, we obtained the crowding regime at rather high voltages and more pronounced profile asymmetry with increasing differences in the ionic sizes.