You can use the SAPUI5 Visual Editor to replace the default icon by any SAP icon.
In the object page's header, the header image is an avatar control. By default, the avatar is rendered as a square. If the avatar's source, initials, or icon isn't set or found, a fallback placeholder is displayed. The type of placeholder depends on the shape of the avatar. If the avatar is circular, a person icon is shown. If the avatar is a square, a product icon is shown.
Please note that this topic has not yet been updated with information specific to OData V4.