Change Product type's referenced Variation type Once a Product type is created, I cannot change Variation type in Product type. Is this a feature, or is there a way to change it?

Is it safe if I change it in the database?

This is useful because I want to use entity_clone and create multiple similar Product types and change the variation type after the clone.
It's safe as long as you don't have any products. We need to change the logic in Commerce so that it checks for existence of product entities, instead of just checking whether the product type is new. Continued in your issue: https://www.drupal.org/project/commerce/issues/3014686