(Yb,Tm)B12 is a new series of compounds based on the archetype Kondo insulator YbB12. The systems with moderate concentration of Tm demonstrate a considerable enhancement of the thermoelectric power that seems to be related to the magnetic properties of the material. Recently we have studied the high-energy (above 35 meV) dynamical magnetic response in (Yb,Tm)B12. Here we propose to trace the evolution of the spectral response in Tm0.93Tm0.07B12 and Tm0.85Tm0.15B12 in the energy range below ~25 meV, where the spin gap along with cooperative near-gap-edge excitations have been observed in the undoped YbB12. For the precise quantitative subtraction of Tm contribution we further plan to measure the samples Lu0.93Tm0.07B12 and Lu0.85Tm0.15B12, whose magnetic response represents the Tm contribution only.We estimate that 7 days of beam time in total are needed to collect the data with reasonable statistical accuracy, including the detailed study of the temperature dependence, measurements of the background, of the nonmagnetic reference compound LuB12, and of the vanadium standard.