Hi,
No, if you change the name of a product variant, or even a value of a characteristic, it won't change the id of the variant/product and thus won't be a problem for the reorder system.
But if you delete the variants, the products, or remove the characteristics from the product and the add them back, the elements will be deleted and new ids will be assigned to the new elements and thus the system will not be able to add the elements of previous orders in the cart for a new order as these elements won't exist anymore. And you don't want your customers to be able to purchase things that you're not referencing anymore.
It's normal that the address is not copied on reorder. Remember that it is a "reorder" button, not a "copy" button.
When you use the copy button of the backend, yes, you'll have a new order with all the elements from the original order in the new order.
But with the reorder, the system has the user go through the checkout again. That allows him to select/enter another address, add more products if necessary, select a different shipping method, etc. That is necessary.
Suppose that you purchase something on such website, move to a different place and reorder a previous order. If you were not able to change the address of the new order, the goods would be delivered to an address were you don't live anymore.