Change right_command to hyper key (f19 when alone). Change right_option to fn.

a.json

{
    "description": "Change right_command to hyper key (f19 when alone). Change right_option to fn.",
    "manipulators": [
        {
            "from": {
                "key_code": "right_option",
                "modifiers": {
                    "optional": [
                        "any"
                    ]
                }
            },
            "to": [
                {
                    "apple_vendor_top_case_key_code": "keyboard_fn"
                }
            ],
            "type": "basic"
        }
    ]
}