If you need to change your embouchure position, you'll have to give your chops time to ease into the new position by playing very easy music in the beginning. If you just try to play the same music as before, it most likely won't work and you'll end up very frustrated and you might even hurt yourself.
Many people are unsuccessful at changing their embouchure position because they are too eager to play high, fast and loud immediately. The fact is that your chops need time to adapt and they won't adapt well if you rush them. Take time to play even beginner exercises for the first few days and gradually increase the difficulty level over the next few weeks. The change should be much smoother this way.
I am associate principal horn of the Singapore Symphony Orchestra and the author of the progressive methods. I'm happy to share my experience as a horn player and teacher with you.