We probe the reversible thermal solidification of crowded solutions of colloidal star polymers in a marginal solvent upon addition of linear homopolymer chains consisting of the same monomers, and for two different linear polymer molecular weights we find that they have a dramatic impact on this phenomenon. If the linear chain molecular weight is much smaller than the star arm molecular weight, penetration is favored, the stars swell (the linear polymer solution acts as a good solvent for the stars), and the jamming temperature drops for a given star concentration. On the other hand, if the linear chain molecular weight exceeds that of the star arm, the stars shrink and the mixture exhibits liquidlike behavior over a wide range of star concentrations and temperatures. These results offer new possibilities for molecular control of the flow properties of soft colloids.