I was VERY specific with you on this, I will state it one more time:
You DO NOT have to attend a "lower" course by UTI to attend ELITE training. I can't say this for sure about Porsche training. You only need to attend a course which the Custom Training Group recognizes (NATEF Master Certified Automotive programs).
From what I understand, you'd need to decide which one you want to go to, MB or Porsche, as you need to sign a letter of intent to get into the MB program, and I would guess Porsche requires the same thing. With MB you'd need to agree to work for a dealer for a year also.
I'd also state you don't get "license" to work on the cars.
The prerequisite courses are usually 2 year programs, are you in a position where you can go to school for 2 years before getting into one of these classes, and would you really be willing to go through that, given you've been working on them 8 years and know them inside and out?
I guess I'm confused on what you are seeking. Again I've been a dealer tech almost 10 years, I have no "license" yet, there is none. If you want to get into MB or Porsche manufacturer training, get a job at a dealer, they will send you to training.