You can add tEXT chunks with the SetAttribute method of MagickImage:
using (MagickImage input = new MagickImage("logo:")) { input.SetAttribute("Magick.NET", "Rules"); using (MemoryStream memStream = new MemoryStream()) { input.Write(memStream, MagickFormat.Png); memStream.Position = 0; using (MagickImage output = new MagickImage(memStream)) { string rules = output.GetAttribute("Magick.NET"); Console.WriteLine(rules); } } }