How to keep caramel from hardening prematurely? Let me be clear: I am NOT making a recipe where I want the caramel to stay soft and gooey. The end result is supposed to be hard like toffee or peanut brittle. But everything I search seems to be for how to keep caramel in a soft and gooey state, so I just want to be clear that's not what I'm after.

I decided to shake up my recipe, by pouring it into holiday-shaped molds instead of breaking apart a giant slab. The problem is my molds will not hold all the caramel at once, so I'll have to mold it in batches.

So can anyone tell me how to keep the remaining caramel from solidifying before I'm ready to pour it? Ideally without turning it into a lump of charcoal?
I'm sorry, but what you are asking for is not possible. Caramel is a hard substance (I mean pure caramel here, not the stuff which has added dairy or acid and never hardens). You cannot even keep it melted the way you can do with water, because its decomposition temperature is lower than its melting temperature - at temperatures at which it is liquid, it is not staying chemically the same, but progressing to charcoal. 

So, you have to buy more molds, or make your recipe in several batches. But you can't just keep liquid caramel around until your molds are ready to reuse. This would be breaking the laws of physics.