Hi Mehrshad,
Welcome to Microsoft Community.
It's great to hear that you're exploring different configurations with your Surface Book 2. In general, attaching a tablet with a Core i5 CPU to a keyboard base with an Nvidia GPU designed for a Core i7 tablet should work without any major issues.
There are no documented issues or restrictions from Microsoft that prevent mixing a Core i5 tablet with a GPU-equipped base. If you don't experience any issues with this setup, then you can go ahead and use it, but there may be some potential driver compatibility issues.
If you have any specific concerns or encounter any issues in the future, feel free to reach out for further assistance. Your SincerelyHahn. W - MSFT | Microsoft Community Support Specialist