replace or update json child with golang without converting json to struct

I need a generic way do modify Json files. I would like to build an API tester. Don't want to corvert json -> structs. I want to iterate over files like json file a and update my dummy request json file b.

I used regex replace for children on the first level to test string parameter for example. But for nested children I thought it would be nice to generate small json files with the parameter to test and update the dummy request with those patches. What would be the best way to achieve this with go?

json file a

{
"params": [
{
  "human": {
    "men": {
      "a1": "x",
      "a2": 1
    }
  }
}
]
}

json file b

{
"typed": false,
"params": [
{
  "foo": "bar",
  "human": {
    "men": {
      "a1": 36,
      "a2": 36
    }
  }
  "fooooo": [
    "bar"
  ],
  "fooobar": "1234"
}
],
"mode": "online"
}