using System;

public class Program

{

    public static void Main()

    {

        var json = @"{'ID': 7,  'T': 1511819861, 'E': 777,'ET': 2,'DEVID': f525873c,'DEVTS': 1511801849}";

        Console.WriteLine(FixJson(json, "DEVID"));

    }

    public static string FixJson(string json, string property) {

        var index = json.IndexOf(property);     

        var indexColon = json.IndexOf(':', index + 1);      

        var indexComma = json.IndexOf(',', index+1);        

        var val = json.Substring(indexColon+1, indexComma - indexColon-1);      

        var replace = string.Format("'{0}': {1}", property, val.Trim());        

        var forR = string.Format("'{0}': '{1}'", property, val.Trim());     

        return json.Replace(replace, forR);

    }

}