Copying variations from one product to another

You can duplicate the whole product: https://cld.wthms.co/18Rv3/17jz25wz

So what if you have 100 products each with a small, medium & large size and you want to add X-large to the sizes. Do you have to go to each product 1 by 1 to update? Or say only 1/2 of your existing products are going to get the additional size or maybe an additional color, how could you add a variation to only specific products?

Just curious how you deal with a large store with 100’s of items with different size & color variations?

thx!!