As you know, when you insert a core, it says free. Why not make an option for removing the core? Removing the core could be given a cost, relative to the varium or credits you spent on it. Maybe half the price of what you spent on the core? Or maybe even full price. Once the core is removed, you can place it into another item. This would of course not work for locked cores, as they are locked.
Whats the point of it if it is full price? I'd only support if it is half the price or none. And something very simular (making the removal free) has been suggested many times before.
No no no, this would nearly negate the purpose of removing cores if you could just buy them again after destroying them for the same price. The only benefit I see from full pricing would be to keep rare, unlocked cores that are not available for purchase anymore. Not charging anything to simply move a core but maybe put time restrictions for ease on the database.
I'm a bit tired and my math was clearly off in my head when I typed that, I thought it would somehow save you money doing that somehow. My mistake indeed. But heck, I'd be okay with a 75% removal cost.