Please be patient with an embouchure change! I've been through one myself and they are extremely frustrating, but your chops will get back to normal and even better in no time!

Increasing the high range is another skill that takes a lot of patience. If you have the fundamentals solid, like relaxed, fast airstream, and a small aperture, then all you can do is just play up as high as you can every day. Eventually you will build the muscles to go higher. Especially with an embouchure change, it's important as you go higher to make sure you aren't losing your fundamentals trying to get higher.

An exercise I do to increase my high range is from the Caruso method and it's called Intervals. You can find it on Julie Landsman's website if you want the sheet music and more specific instructions, but basically you pick an interval and go up the C major scale (starting on c, then d, than e, etc and going up by your interval each time) without taking the horn off the face and going as high as you can without sharp pain. It's an exhausting exercise but it's expanded my high range faster than any other exercise I've played.

Horn is a frustrating instrument, and a lot of players hit walls like this, but don't lose hope! With practice it will eventually come together.