We propose to study the evolution of the spectral features in the dynamical magnetic response in series Yb_{1-x}Tm_{x}B_{12} (x=0.15, 0.6, 0.8). Tm doping results in non-trivial enhancement of the thermoelectirc power when tuning Yb(Tm)B12 from Kondo-insulating to antiferromagnetic regime. The dynamical response of YbB12 has specific spectral features and details of its transformation with x supposed to the key for understanding thermoelectric power enhancement. Basing on our experience on HET and taking into account the performance of MERLIN, we estimate that 5 days will be required to determine the overall structure of magnetic excitation spectrum at tempeartures between 5 and 250 K for 3 samples, and to get the first information about magnetic dispersion al low temperature for one of them (Yb0.85Tm0.15B12).