<p>using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading;
using System.Threading.Tasks;
using System.IO;
using System.Xml;
using System.Text.RegularExpressions;
public static class GlobalExtensionMethods
{
  public static string Replace(
    this string source, 
    string oldValue, 
    string newValue, 
    StringComparison comparisonType)
  {
    StringBuilder sb = new StringBuilder();

    int previousIndex = 0;
    int index = source.IndexOf(oldValue, comparisonType);
    while (index != -1)
    {
        sb.Append(source.Substring(previousIndex, index - previousIndex));
        sb.Append(newValue);
        index += oldValue.Length;

        previousIndex = index;
        index = source.IndexOf(oldValue, index, comparisonType);
    }
    sb.Append(source.Substring(previousIndex));

    return sb.ToString();
  }
}

</p>