Triton and Sedna, new toys I made. Advice needed

I made 2 new toys. I still have a lot to learn. The bicolored green one (Triton) feels actually really nice. I need to rework Sedna. If anyone is available to give advice, I am planning on perfecting these designs, make more symmetrical, etc,... so my plan is to use the toy to cast a plaster model and then in order to save on sillicone, slash the older mold in half, separate a few inches and use it as a filler when I pour the new mold. Do you think that’s a good idea? My main concern is that the cured and new silicone may not stick together so well. Help!!!!