FERPA

Hello everyone,
I understand that not waiving rights in regard to FERPA could come off as a red flag to admissions officers. However, one of the teachers who has agreed to write my letter of rec allows students to proofread and offer further details to be added to the letter which he will determine significant. Does this mean I am unable to waive my rights?

In other words, I am asking does waiving rights mean I cannot see the letter after it has been submitted only or before and after the admissions process?