storemaker

Thank you for answer. I’ll probably develop a custom plugin using yoast’s API.

You can resolve this ticket.

Yes, you can change ratings manually.
Values are saved in the wp_postmeta table.
You have to look for _kksr_casts, _kksr_ips, _kksr_avg, _kksr_ratings.

Yes, you can manipulate the star ratings.
The values are saved in wp_postmeta table.
Filter values with prefix _kksr from the table and you are free to change anything.

Although, I do not recommend to change ratings drastically, Google might see it as unnatural.