One of the reagents (a byproduct actually of the curing process for silicone caulking) is acetic acid (vinegar), which stabilizes the plasticizers. Just a hair

One of the reagents (a byproduct actually of the curing process for silicone caulking) is acetic acid (vinegar), which stabilizes the plasticizers. Just a hair more makes it a little more "pliable" for a little while longer while you mold the final product in my experience. You only need a tiny bit, a dilute spray bottle of white vinegar is enough -- It's useful for other things too. YMMV, it appears to be dependent on what style of silicone caulking you use.