using System;
using System.Collections.Generic;
using System.Text.RegularExpressions;
public class Test
{
	public static void Main()
	{
		var s = "(Price+Discounted_Price)*2-Max.Price";
		var dct = new Dictionary<string, string>();
		dct.Add("Price", "A1");
		dct.Add("Discounted_Price", "A2");
		dct.Add("Max.Price","A3");
		var listAbove = new List<string> { "Price", "Discounted_Price", "Max.Price" };
		var result = s;
		foreach (string phrase in listAbove)
		{
			result = Regex.Replace(result, @"\b(?<![\w.])" + Regex.Escape(phrase) +  @"\b(?![\w.])", dct[phrase]);
		}
		Console.WriteLine(result);
		//var res = Regex.Replace(s, @"(?<![\w.])[\w.]+(?![\w.])", 
			//x => dct.ContainsKey(x.Value) ?  dct[x.Value] : x.Value);
		//Console.WriteLine(res);
	}
}

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