using System;
using System.Linq;
using System.Text.RegularExpressions;
 
public class Test
{
	public static void Main()
	{
		var s = "#Abc=\"\"";
		var result = Regex.Replace(s, "#[A-Za-z0-9]+(=\"\")", m=> 
		    string.Format("{0}{1}{2}", 
		       m.Value.Substring(0, m.Groups[1].Index),
		       new string('?', m.Groups[1].Length),
		       m.Value.Substring(m.Groups[1].Index+m.Groups[1].Length, m.Value.Length-m.Groups[1].Index-m.Groups[1].Length)));
		Console.WriteLine(result);
	}
}

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