I'm including a video of me feeding George treats. He used to be over-eager about snatching treats from one's hand, as were a couple of other horses here. I've found the solution to be a) feed more treats, and b) ask him to move his mouth away from the treat-holding hand before I give it to him. Moving his mouth just a half an inch is enough - or even just having the thought of moving it. I'm feeding treats with one hand and holding my phone with the other, so it's very wobbly, but you can see at least one instance of him obviously moving his mouth away at around 14-17 seconds. I'll be able to dispense with this exercise pretty soon, I think.
Since I've been being nice to him, he's not that keen on rejoining his buddies. Here he is standing by the gate after I left to take Chloe and Bridget out--
After Chloe and Bridget's grazing walk, a thunderstorm was threatening, so the horses were all brought in. I brought the mounting block into Chloe's stall and sat beside her while she dozed. Her door was open, and after a while she ventured out to graze beside the barn. When it was time for her to come in, I walked out and called her name -- she turned around and came right back in to her stall. I can't get over the transformation in this little horse. But of course it's not really her that's changed - it's me.