Can I advertise that I am certified in the Muscle Release Technique℠ after I take one of Michael’s workshops?

No, Michael does not teach a certification workshop.  You can certainly advertise that you trained under Michael Young and that you took his workshop to learn the Muscle Release Technique℠.  Since the Muscle Release Technique℠ is a trademarked technique, you simply need to put the symbol for the trademark (which is SM since this is a service) each time you use the words Muscle Release Technique℠ in print.