You don’t need to worry about any implications by manually creating the Message Class file. I am not sure why the message class not added by the installer to your machine.
Could you please send the Formativ Configuration to email@example.com. You can obtain the configuration by selecting Help | About Formativ… from the GroupWise main menu. When the About Formativ dialog appears, go to the Configuration tab and click the button Copy to clipboard. Then paste the text into your email (or save it to a plain-text file and include it as an attachment).