using System;
using System.Collections.Generic;
using System.Text.RegularExpressions;
 
public class Test
{
    public static void Main()
    {
        Dictionary<int, string> dict = new Dictionary<int, string>
        {
            {1, "foo1"},
            {3, "foo3"}
        };
 
        String text = @"%%%% START %%%%
 
sit amet ipsum sagittis luctus eu id diam. 
[%RC:3%]
 
Morbi suscipit iaculis accumsan. Morbi laoreet consectetur nisl, luctus tempor felis ultrices commodo. Praesent dui augue, interdum non rutrum vel, vestibulum sit amet lorem. Nam sit amet erat elit, et porta mi. Vestibulum non urna magna. Phasellus pharetra rutrum urna quis tincidunt. Duis metus quam, fermentum sed ultricies id, tincidunt id ipsum. 
 
[%RC:1%]
 
%%%% END %%%%
";
        string result = Regex.Replace(
            text,
            @"\[%RC:(\d+)%\]",
            match => dict[int.Parse(match.Groups[1].Value)]);
 
        Console.WriteLine(result);		
    }
}

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