A. The only field required to maintain product sync connection is the Identifier on Shopify (Barcode or SKU - Depends on user settings) and the Product code on Smaregi. If this field matches in both platforms, products can have different information.
For product images, if the "Product image" setting is toggled OFF in both platforms, users can maintain / add different images for each platform.
In order to add different product information (*excluding the Barcode/SKU and Product code), simply connect the products and toggle the Product update sync feature OFF and change information - which will not be synced as product updates are inactive.