Localized surface plasmon resonances (LSPR) make systems capable of concentrating and amplifying light intensity at their near surface. Applications ranging from energy harvesting to biological sensors depend on the modulation of LSPR. Through the synthesis and shape modifications of Au quasi-triangular nanoplatelets (QTP) arrays, LSPR modulation from near-to mid-infrared (~1.5μm to ~4.5μm) is revealed. Au QTP arrays are then associated to a thermochromic vanadium dioxide (VO2) layer leading to a "smart" nanocomposite exhibiting modulated absorptions. The VO2 layer acts as a phase change material with a tunable dielectric function vs. temperature and represents an active matrix. The dynamics of the geometric changes in QTP arrays and the phase transition of the matrix are directly correlated to the shift of the LSPR position (Delta l_SPR ~ 675nm). The experimental data are supported by a theoretical approach via the finite difference time domain (FDTD) method that provides the LSPR characteristics in the various Au QTP array and nanocomposite configurations. The experimental and modelling investigations prove that the red-shift resonance modulation originates from the creation of a temperature-dependent core-shell structure of Au QTP (core) surrounded by a thin metallic VO2 layer (shell) and embedded into the VO2 dielectric matrix.