Several weakly deacetylated glucomannan gels (pH = 9.1), at a concentration of 5 g/100 mL, were subjected to high hydrostatic pressure (HHP) at 0, 100, 200, 400 and 600 MPa. They were frozen and stored at −20 °C for two years to study the influence of long-term frozen storage on the rheological properties of pressurized samples (FP100, FP200, FP400, FP600) compared with a frozen unpressurized control (FP0) and an unfrozen unpressurized control (P0). In unpressurized gels, frozen storage reduced stress (σmax) and strain (γmax) amplitudes while forming a more solid-like network (FP0 vs P0). Gel FP0 maintained the rubber-like response from temperature (T) > 70 °C as in P0. HHP reduced loss of conformational stability and enhanced cohesiveness in FP100−FP600 vs FP0. Particularly, 400 MPa improved the degree of connectivity in the glucomannan (GM) network producing a better thermoset response at T > 70 °C (FP400).