Welcome to Shopify Community. My name is Olivia and I work here.
Thank you for sharing your question with our network. Since you don't want to publish your app, have you considered creating a custom or private app to work with your exclusive stores?
After you enable private app development from the Shopify admin, you need to generate the required credentials from the Shopify admin of the store that you want to connect with your app.
From your Shopify admin, go to Apps.
Click Manage private apps.
Click Create private app.
In the App details section, enter a name for your private app and a contact email address.
Shopify uses the email address to contact the developer if there is an issue with the private app, such as when an API change might break it.
In the Admin API section, select the areas of your store that you want the app to be able to access.
If you want to use the Storefront API, then select Allow this app to access your storefront data using the Storefront API.
- In the Storefront API permissions section, select which store data you want to expose to the app.
Four permissions are selected by default: Read products and collections, Read and modify customers, Read and modify checkouts, and Read blogs and articles.
When you're done, click Save.
The API key and password for your app are now displayed on screen.
After you have the required credentials, the private app can access your store's data.
I trust this should work for you, but if you have further questions don't hesitate to let me know.