Change default page dimensions with .json theme.

Is it currently possible to change the default width & height of a report page using a .json theme? There are attributes such as pageSizeWidth in the schema, but they do not seem affect the report. I have tried the following:

"visualStyles": {
        "page": {
                "pageSize": [
                    {
                        "pageSizeTypes": "Custom"
                    },
                    {
                        "pageSizeWidth": 2560
                    },
                    {
                        "pageSizeHeight": 1440
                    }
                ],

The use case is that themes may contain different default font sizes & other visual attributes that do not work well with the default page dimensions. And so it would be helpful if default page dimensions can also be provided by the theme file.