Rename through python

Looking furter into this, I discover that what I need specifically is to use an existing preset, but to set a unique file path. For whatever reason, once I load a preset, I can't change it's file path. I either define a completely new preset through json, or I use an existing one, I can't proceedurally change the filepath of an existing one. 

Could someone please supply an example of how I would do that? 

Say I want to load: 

export_preset = substance_painter.resource.ResourceID(context="starter_assets", name="PBR Metallic Roughness")
stack = substance_painter.textureset.get_active_stack()

Then I am setting that preset but attempting to change each maps output path:

export_config = {
            "exportShaderParams": False,
            "exportPath": "W:/test/monolith/Substance/Painter_Auto_Export/",
            "defaultExportPreset": export_preset.url(),
            "exportPresets": [{
                "name": "PBR Metallic Roughness",
                "maps": [
                    {"fileName": "/Painter_Auto_Export/NewName_color(.$udim)"},
                    {"fileName": "/Painter_Auto_Export/NewName_metalness(.$udim)"},
                    {"fileName": "/Painter_Auto_Export/NewName_normal(.$udim)"}
                        ]
            }],
            "exportList": [{"rootPath": str(stack)}],
            "exportParameters": [
                {
                    "parameters": {
                        "fileFormat": "png",
                        "bitDepth": "8",
                        "dithering": True,
                        "paddingAlgorithm": "infinite"
                    }
                }]
        }

The result is that I get output paths that are defined by the PBR Metallic roughness preset, but I need paths that are unique to my map settings. I'm trying to override them as it were.