Thanks for reaching out to the Auth0 Community!
Importing the tenant.yaml file on a free tenant should work provided that you test only the features that pertain to the Free subscription level. This should not incur any additional costs.
Let me also add that creating new fresh tenants will have a Trial subscription which allows the tenant to use paid features for 21 days, after which they are only allowed to use free features.
I hope this helps!
Please let me know if you have any additional questions.
Thanks,
Rueben