I actually had to read over this sentence many times to even begin to understand its meaning. And even after I did that, I was still pretty confused, but this is what I came up with:
Students can give their instructors written consent to have their grades posted by partial UH number. Students who decline to have their grades posted must be given a reasonable means for receiving their grade.
If seeking written permission to post grades by partial UH Number, student's who decline to have their grades posted must be provided with a reasonable means for receiving his/her grade.
As the "sentence" was, I couldn't tell who was seeking permission and from whom that person was seeking it, so I defined the subject as students giving consent to their instructors. I chose "consent" because it seemed clearer to me than "permission" for some reason.
I also changed the pronoun for "students" from "his/her" to "their" since "students" is plural. And obviously the apostrophe in "students" is incorrect since it's plural and not possessive.