My horse does auto changes, but a horse I trained for a bit really needed a good, supportive outside leg to help him change in the back. If he didn't get a good change in the back I'd just tap him with the crop while still really keeping my outside leg back a little and strong and he'd hop/occasionally buck into it. A lot of it was that he was rusty and hadn't been asked to do anything like it in a while.
I firmly believe that every rider should know how to get the correct lead on landing, so changes aren't necessary. It generally varies from person to person and from horse to horse, but I just shift my weight slightly in the air and as soon as we start coming out of the arc of the jump I push inside leg to outside rein in the direction I want to go. It takes some practice, and you really need to be totally secure in your position, but I prefer it especially when a horse doesn't do auto changes, because there are so many little nuances and slightly different methods to teach a horse the cue for a change. Especially when I'm doing sale videos for people and hop on their horse first time. I'm expected to make the horse look good and bad changes never look good, lol.
"Always be yourself. Unless you can be a unicorn. Then, always be a unicorn."