using System;
using System.Text.RegularExpressions;

public class Test
{
	public static void Main()
	{
		string str = "= Fields!Change_Date.Value & Fields!Change_User.Value";
		string result = Regex.Replace(str, @"^= Fields!(\w+)\.Value & Fields!(\w+)\.Value$", "$1 && $2");
		Console.WriteLine(result);
	}
}