Best way to structure / implement / set up models

For a new project I'm planning to start I'm struggling with the following thing. My plan is to deliver a feed with a lot of default products (let's say 75000). These products are all maintained by myself (images, titles, descriptions, prices, etc.)

Clients of my feed can login to the system and I want my clients to be able to modify / overwrite the default values of a product.

Now it would be really easy to just create a User -> Product relation. But this will make it really hard for me to change the default value of a product. This will also mean that if I have 100 clients the database will get very large.

I would like to know whats your view / suggestion on this and how you would implement this.

Thanks in advance.