Export and import all the modules & widgets into a new project?
You could use ModelShare to export your microflows and then import them in a 5.19 model again, but that's about as far as you can get in re-using a model of Mendix version x in Mendix version x-1.
As new model properties are introduced and older ones removed, opening a newer model in an older Modeler would irrevocably lead to corrupt models.
The thing I don't quite understand is why the model needs to be in 5.19 to be deployed from your company server?