Hi Ernesto:

You can inherit and extend the unlink function in the base Model class if you want this across the board. Here's a link to the code in the base class.

https://github.com/odoo/odoo/blob/13.0/odoo/models.py#L3299

If you want this to apply only to specific models, you'll need to extend this function in the classes of those models instead of the base Model class.

Regarding your second question, these changes will apply across the board i.e. form view, list view, import, api, custom code, etc.