I have two diamond chest armor items.

1 has a trim, the other does not.

If I place the trimmed armor in a slot (in the inventory, a chest, etc), move it somewhere else, then place an untrimmed diamond chest in the slot I initially placed the trimmed one in, the icon for the untrimmed chest will change to trimmed.

It does not actually change the item, just the icon. The icon goes back to normal when you move it to another slot