You can run the whole import with PaddleSubs set to the sandbox Environment, for example on a demo site, before you use PaddleSubs for real. A sandbox import works exactly like one into production: it creates its products and prices in your Paddle sandbox, and its Access Subscriptions are attached to them.

The two environments are kept apart. What a sandbox import made is remembered for the sandbox only, so importing the same source into production later creates its own products, prices and Access Subscriptions instead of taking over the sandbox ones. Previous imports lists the imports of the environment PaddleSubs is set to, and an import can only be continued or undone in its own environment.

Accounts are not part of an environment: an account a sandbox import creates is a real account of the site, and an import into production later finds it by its email address. Undo the sandbox import before you switch to production if you don't want to keep them; see the section called “Undoing an Import”.