If you open the model molecule.mdl in as a regular model you will be able to edit the different equations. If you look at the equation for Trad Coflow you will see that is has the comment:
#Tcoflow.mdl#
If you want to add molecules to the list just put them in the model molecule.mdl and then reference their names as shown. It is also permissible to nest definitions of molecules in this manner.
