Hello everybody,   I want to add a constraint but I don't have the idea of how to do it. I created a custom export which auto-generates external ids for each record I export. The export contains a list of students which the lecturer has to update their marks.. and re-imports the same excel sheet which also updates the marks of the students. 

However much there is some information which I don't want the lecturers to update but I have failed to restrict the lecturer from importing the data in case those field values have been updated. 

Any Ideas,  Thank you.