Final answer:
To modify hover details for a custom object called Position, a developer customizes the Position mini page layouts, which determine the fields displayed on hover in the interface.
Step-by-step explanation:
To modify the contents of the hover details for a custom object called Position in a CRM platform like Salesforce, a developer would customize the Position mini page layouts. The mini page layout controls which fields are displayed in the hover details. It is part of the object's page layout configuration, and allows the developer to select which fields are included and their order of appearance when a user hovers over a record's link in the Salesforce interface.