Brandcast does allow you to copy-paste, but you can also easily duplicate elements by <option>-dragging them.
Duplicating an Element to the Same Page
To duplicate an element, hold OPTION (Mac) / ALT (PC) while you click and drag to make a duplicate.
You'll see the cursor change to indicate the number of elements you are duplicating.
Drag to the location you want to place the duplicate item.
Duplicating to Another Page or Site
If you need to reuse an existing element on another page, there's a simple method for duplicating it.
Open both pages as separate tabs in the studio.
Select the element(s) you want to copy.
Click and drag to make a duplicate. You'll see the cursor change to indicate the number of elements you are duplicating.
Keep holding this while you drag your cursor up to the top tabs, and hover over the page you want to duplicate the element to.
After a few seconds, the studio will switch to the page you're hovering over. You can then drop the duplicated element wherever you want.