Key signature change at repeat

I have a piece that includes D.S. al Segno. That measure is in a different key than the Segno and needs to end with a key signature change. I've not found how to do this. I note in the manual how to change the key signature mid-measure, but I tried doing it on the last note of the measure and it changed the key signature for the entire measure, so I'm not sure that feature is working correctly.