Custom Shopify Group Shipping

I need a developer who can make a very specific change to my Shopify checkout flow: when a shopper chooses the “Group Shipping” option, the delivery address must automatically switch to the address I’ve assigned to that product’s collection. I have between 11 and 50 collections right now, each with its own pre-set drop-off location, and the list of those addresses is already prepared.

I’m happy to maintain the mapping myself, so please build the logic in a way that lets me manually pair a collection with its address—metafields, an app block setting, or any clean admin UI is fine as long as it’s straightforward to update later.

The solution needs to:
• Detect the chosen shipping method at checkout.
• Look up the product’s primary collection.
• Overwrite the customer’s entered shipping details with the matching address.
• Work seamlessly on desktop and mobile without disrupting other shipping methods.

Please use standard Shopify tools (Checkout Extensions, Functions, app proxy, or compatible theme code) so everything stays update-proof and within platform policy. At hand-off, I’ll need the working feature installed on my live theme plus concise documentation showing where to adjust the collection-to-address pairs.

My shopify plan is Grow so the limitations of this plan will need to be considered.