In Google Merchant Center you are not restricted to only one website. If you are a merchant or an individual that owns several different websites, you can request a multi-client account.
Having a multi-account will allow you to add multiple domains and also have distinct merchant names for each added domain.
The only requirements are:
If you own one business with multiple countries TLD’s (top level domain ie: .com. .fr. .uk), than to target each Google Shopping country requires you to register these TLD’s to a new account. Instead of creating multiple Google accounts with a new email address, you can simply use one account (multi-account) to register all the websites.
If you are a marketplace owner you can then register an account for each of your marketplace resellers.
Agencies can also benefit from a multi-account when managing client accounts