yes, it is possible.
you can do this by.
- first read the content that is sotred in cache. (stored content is in key value pair)
you can do this by
var storeObj = window.localStorage;
var string = storeObj.getItem(storeKey);
// this will be string
parse it into json if you want that.
json = JSON.parse(string);
* now append yor result as by string or by json.
// if by json
json["item"] = "newvalue";
now clear storage by key
storeObj.removeItem(storeKey);
now store back this new json to cache
storeObj.setItem(storeKey, JSON.stringify(json));