Selecting a template to use:

Insert model attribute with value of name template in options.json Master.

Example:
{    
    "plugins":{
        "template":{      
            "model":"default"
        }
    }
}

Selecting a part to page unity:

Insert model attribute with value of name template in options.json of page.

Example:
{    
    "plugins":{
        "template":{      
            "part":"pages"
        }
    }
}