sample.py

import json
import copy


def read_json(file_path):
    with open(file_path, "r") as file:
        data = json.load(file)
    return data


def write_json(file_path, data):
    with open(file_path, "w") as file:
        json.dump(data, file, indent=4)


def edit_json(food_dict):
    """nameの値を小文字に変換"""
    edited_data = copy.deepcopy(food_dict)

    for data in edited_data.values():
        data["name"] = data["name"].lower()

    return edited_data


def main():
    file_path = "sample.json"
    food_dict = read_json(file_path)
    edited_data = edit_json(food_dict)
    write_json(file_path, edited_data)


if __name__ == "__main__":
    main()

sample.json

{
    "food1": {
       "name": "APPLE",
       "price": 150
    },
    "food2": {
       "name": "BANANA",
       "price": 100
    }
 }