I think Guidance only works in 'Team Member Formulation Requirements (from Project Template)' section. if the project is in edit mode and you click 'Update Team Members', you will be able to modify the 'Guidance' field. however, this field doesn't show in 'Additional Team Member Formulation Requirements field.'
I think I was not great at explaining.
Please create a brand new project and go to PROJECT TEAM Tab.
Please go to Team Member Formulation Requirements (from Project Template) and add a functional area and a user under "team members" TAB.
System doesn't still prevents me from editing the guidance field.
If I try to populate the same field in Project templates, I do nt have any problem.