Yes!

If you'd like lower your IUA (eg from $1,500 to $1,000) you have a 30 day window of opportunity on your annual anniversary date.  So if you enrolled on October 15th for a November 1 start date, each October you could make an IUA change.

If you would like to raise your IUA (eg from $1,500 to $,2500) that can be done on your enrollment anniversary as described above, or you can utilize an exception to raise your IUA once at any time during the enrollment year.