Cmd+Tab remaps to Ctrl+Tab
Here is the JSON to remap these keys only.

{
  "title": "Cmd+tab maps to Ctrl+tab",
  "rules": [
    {
      "description": "Make Cmd+tab activate Ctrl+tab",
      "manipulators": [
     {
        "type": "basic",
        "from": {
            "key_code": "tab",
            "modifiers": {
                "mandatory": [
                    "command"
                ],
                "optional": [
                    "shift"
                ]
            }
        },
        "to": [
               {
                "key_code": "tab",
                "modifiers": ["control"]
               }
        ]
      }
      ]
    }
  ]
}