CommandSnippet provides control of the Commands object. You use the method AddCommandSnippet() to insert a new child command snippet in the project tree:

sol = Model.Analyses[0].Solution 
cs = sol.AddCommandSnippet()
cs.Input = "/COM, New input"
cs.AppendText("\n/POST1")

You can also use ImportTextFile(string to import content from a text file or use ExportTextFile(string) to export a command snippet to a text file.