Matrixify

This app is by far the best app I used on Shopify. It is a bit pricy if you have a large inventory but definitely worth it because it covers everything that you would expect Shopify to cover in the first place, when it comes to updating any part of your store.

They also have state-of-the-art documentation and super responsive customer communication. I know I sound like a little fake when I write like this but I am sure you will understand me once you start to use their services. I am a big fan now, after interacting with them on and off since last year.