Yes! You can edit or add pictures of products without any problem. It is even recommended to do so in order to personalize your shop as much as possible.
Above all, remember to link your new pictures to your variants.
Here are the steps to follow on Shopify:
1. Click on the product color you want to link to the photo added beforehand.
2. Click on "Actions", then on "Update images".
3. A small window opens, just choose the image to link with the color/variant and save.