using System;
using System.Collections.Generic;
using System.IO;
using System.Linq;
using System.Text.RegularExpressions;
 
public class Test
{
	public static void Main()
	{
    	var line = "this.Button.Value\nthis.value\ndocument.thisButton.Value";
    	var word = "this";
    	var rx =new Regex(string.Format(@"(?<=\s)\b{0}\b(?=\s)|\b{0}\b(?=\.)", word));
    	var result = rx.Replace(line, "NEW_WORD");
        Console.WriteLine(result);
	}
}

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