FWIW, I have spent about seven years engineering an embouchure change.
I've done it little by little.
I don't belive that it is pratical for a busy trumpeter to make a drastic change that can cause practical down time. For me it was extremely important to make the changes subtly so as not to loose work with the unavoidable inconsistencies that result from embouchure adjustments.
As it is, I have lost a few gigs due to some problems that occurred as I changed my chops. This was embarassing, painful and a little costly, but it had to be done. One of those gigs was lost due some problems that I had because of incomplete mastery of certain aspects that I was building on. I would blow ocassional "airballs." It was devastating, but I refused to yeild to discouragement. Persistance has paid off in spades, however.
Keep in mind that I began this embouchure change even after a stint
with Maynard and many years of full time professional experience.
I was a busy free lancer in the studios and with jobbing orchestras around
Chicago. I had a pretty strong foundation. I just had a few
bricks that were broken and out of place. These "bricks" were costing
me a great deal peace of mind, however. I was pressing too much.
My chops would get sore. I would ocassionally have to take some time
whether I liked it or not. I would have a bad day now and then. Contractors don't like this. Unfortunately, in the music biz, many of us don't get the luxury of accepting a "bad day." I couldn't continue like this.
Now, some of the details of the things that I have used in improving on the situation are basically outlined in my web site and more to follow in my book. Suffice to say for now, in spite of my experience, it took me six years to fix the problem. While I did loose a couple gigs, I did manage to stay reasonably busy as a free lancer in spite of the changes. Now that things are fixed, my gig load is increasing on a dialy basis. It has paid off, but it was tough.
A complete embouchure change is a drastic thing. IMHO, this is best tackled by a younger player who has nothing to loose from starting over. A seasoned player should make any changes much more gradually. In fact, I feel that the attitude of that player should be to take the skills that he or she already has and build on them - make those skills better by fixing them - rather than discarding them for a new start. This is my approach as a teacher. I would only consdier an embouchure change as an extreme last resort.
I am not sure if I'm addressing this thread very well. If not, I apologize for the misuse of bandwidth. I only offer these ideas as fodder for the cauldron of concepts that we are all cooking up! Brother, what a mixed metaphor!