ADVISER code for returning student until age out
If the student is returning to your district and will continue there until they age out, you will keep the student enrolled the same as any returning student. They would not be exited from enrollment or SPED.
No change would be made to the student's cohort year, but if you want to enter a different year in the Expected Graduation Year field for when you anticipate the student will 'graduate', that is perfectly acceptable. But it will not change the student's Cohort Year. That remains as set when the student was a 9th grade for the first time.