How to "edit" "dynamic" json data with Go?

Last time I asked here how to edit json data without knowing exact struct of that data and I was told to unmarshal it instead regexp because it's more efficient.
I have some kind of "server" which takes wiremock mapping changes it slightly and send back.
wiremock mapping can have different structs -> https://wiremock.org/docs/stubbing/
It can be something like this:

{
"request": {
"method": "GET",
"url": "/some/thing"
},
"response": {
"status": 200,
"body": "Hello world!",
"headers": {
"Content-Type": "text/plain"
}
}
}

but also something like this:

{
"mappings": [
{
"request": {
"method": "GET",
"url": "/one"
},
"response": {
"status": 200
}
},
{
"id": "8c5db8b0-2db4-4ad7-a99f-38c9b00da3f7",
"request": {
"url": "/two"
},
"response": {
"status": 200,
"body": "Body content"
}
}
],
"importOptions": {
"duplicatePolicy": "IGNORE",
"deleteAllNotInImport": true
}
}

and probably something else.

How can I "edit" such dynamic structure? I've written this "parser" for simplest case:

package main
import (
"encoding/json"
"errors"
"fmt"
"io"
"log"
"net/http"
)
var anytype map[string]interface{}
func parseMappings() {
}
func parseReq(req map[string]interface{}) (string, error) {
fmt.Printf("%T %v\n", req, req)
for k, v := range req {
if k == "url" {
if v, ok := v.(string); ok {
return ("/geronimo" + v), nil
}
return "", errors.New("Not a string")
}
}
return "", nil
}
func handler(w http.ResponseWriter, req *http.Request) {
payload, err := io.ReadAll(req.Body)
if err != nil {
log.Fatal(err)
}
err = json.Unmarshal(payload, &anytype)
if err != nil {
log.Fatal(err)
}
fmt.Printf("%T %v\n", anytype, anytype)
for k, v := range anytype {
if k == "request" {
if v, ok := v.(map[string]interface{}); ok {
s, err := parseReq(v)
if err != nil {
log.Fatal(err)
}
// what to do here? how replace url with new value?
// url = s
fmt.Println("Done", s)
}
} else {
fmt.Printf("%v %T\n", k, v)
}
}
}
func main() {
http.HandleFunc("/", handler)
http.ListenAndServe(":8080", nil)
}

but even here I have no idea how to replace url value with new data
// what to do here? how replace url with new value?
// url = s

If you want to replace a URL value in such an input, you have to find the object that contains that URL value, and work with that. Something like this:

req:=m["request"]
if reqMap, ok:=req.(map[string]interface{}); ok {
// reqMap is the object in "request: {...}"
reqMap["url"]=newURL
}

Alternatively, you can use one of the JSONPath libraries out there.