DON'T DO IT! The putty is a clay filler with a thick oil which is too viscous to attack the plastic hull but the initiator is highly corrosive to organic polymers and could cause swelling and softening of the plastic before destroying the polymer matrix from the inside. Chemical initiators are often peroxides and cancause explosions when mixed with organic chemicals in the correct proportions. UV light has already been used as an initiator to set the plastic during the printing process and too much UV light can make the plastic mor brittle (look closely at the deck edges on your model, qhite often these are paler than the main body of the model and more powdery...)
Why on earth would you want to make the model heavier? It will shatter the hull if you drop it. If you leave it light, it will bounce on impact!
Finally, if you add heavy metal, the glue will cause corrosion, and the hull will crack under the expansion of the mass. Look up the history of adding metal inside the polymer maitrix itself; google "resimet".