Is it appropriate to ask my (USAF) Commander?

Yup Im also a Staff Sergeant and if I was in your situation would talk to the CC directly. Also if you get a 3 EPR FIGHT IT. no way 1 incident should turn a 5 into a referal 3. at best it should be a referal 4. The EPR is based on your whole year. So if you were outstanding for 363 days of the year and 2 days you were less than stellar, on average you were still above average (which is 4) just because those 2 days happened to be when the EPR was being reviewed, it is wrong for them to mark you down that much for 1 incident if your overall track record is so good. This is the reason the EPR system is so dam broken. But back on track. Talk to your CC and apologize and explain why you should not be on a UIF. I would do it in a official letter and get letters of character reference from your co-workers/supervisors. But if your not up to date on the Tounge and Quill, or your writing is not that good, then doing it in person is the next best thing.