using System;

using System.Collections.Generic;

using System.Linq;

using System.Text.RegularExpressions;

public class Program

{

    public static void Main()

    {

        string source = "חָזִיתִי כְּמִבַּעַד לֶעָשָׁן בְּקִמּוּרֵי הָרֶסֶס הַלָּבָן";

        Dictionary<char, char[]> exclude = new Dictionary<char, char[]>

        {

            {'\u05db', new char[] {'\u05bc' } }, // כּ

            {'\u05d1', new char[] {'\u05bc', '\u05b7' } }, // בַּ

        };

        string replaced = RemoveDiacritics(exclude, source);

        Console.WriteLine(replaced);

    }

    public static string RemoveDiacritics(Dictionary<char, char[]> exclude, string source)

    {

        string match = "(?<=[א-ת])[\u05b0-\u05c2]";

        string exclusionGroup = string.Join("|", exclude.Select(p => string.Concat(p.Key, string.Join(string.Empty, p.Value))));

        string except = String.Format("(?!{0})", exclusionGroup);

        string combined = string.Concat(except, match);

        return Regex.Replace(source, combined, string.Empty);

    }

}