using System;

using System.Linq;

public class Program

{

    public static void Main()

    {

        var text = """

            aaaaaa

            <!-- {{ LINKS }} -->

            <!-- {{ LINKS }} -->

​

            bbbbb

        """;

        var segment = text.Split([ "<!-- {{ LINKS }} -->" ], StringSplitOptions.RemoveEmptyEntries)

                           .Where(p => string.IsNullOrWhiteSpace(p.Trim()) == false)

                           .Select(p => p.Trim())

                           .ToList();

​

        Console.WriteLine($"Number of segments: {segment.Count}");

        segment.Insert(1, "hello world");

        var merged = string.Join("\n\n<!-- {{ LINKS }} -->\n\n", segment);

        Console.WriteLine();

        Console.WriteLine("Merged text:");

        Console.WriteLine(merged);

    }

}