Gents I have been there, let me tell you how it goes. You install that shiny new part, it turns out it adds 30 hp, it doesn't matter what part it is, just remember that it adds 30 hp. You go in a few months later to get your power mirror fixed afterwards and your warranty works fine and everybody is happy. Six months later your differential grenades from a broken axle shaft also taking out a few suspension pieces. You car is loaded onto a flatbed and finds its way to the dealer. The dealer will look at the damage and ascertain that some of the parts cant be ordered without the approval of a regional rep that works for MB, further they dealer cannot get reimbursed for labor for that job unless the same rep signs off on the repair. That rep, he is well trained, doesn't sell cars, and has absolutely no mercy because his job is to guard the gate. If he decides that your car has had hp added to it he will deny your warranty coverage on that repair. Why? MB built the car and its driveline for the hp it was sold at and by adding hp you have changed the car to a configuration it did not sell you and MB is not obligated to provide warranty coverage on something they did not sell.
So the rep has refused to cover this repair. You will not hear it from him/her because he doesn't work with the public, you will instead get the news from the dealership. They will tell you they are terribly sorry but your car cannot be covered for the reason above. You can now go ahead and spout M&M to your hearts content, you can jump up and down, you can scream, you can make threats, none of it will change anything. Your car is broke down and if you want it fixed you will have to come out of pocket for the time being. If you don't have the money you will have to have it towed to wherever you plan on storing it while you save up the money. All those threats, screaming, they were completely useless because you are not in possession of your warranty coverage, MB is in possession of your warranty coverage and if they refuse to give it to you you must fight or pay.
Lets say you fight. You will need to get an attorney. You have a long process to follow that will vary by state and at best it will be weeks but will probably be longer, it could be the better part of a year if MB digs their feet in and you are determined to go the distance. During that time you will incur many billed hours from your attorney which you can reduce somewhat by doing the legwork yourself but you must then invest your time. When you do get to court if you go that far the M&M act does provide for the ability to ask for fees but you are not guaranteed to get them even if you win. I won and did not get my fees.
This is the reality of what you face. If you have deep pockets it doesn't matter. Whats 20k for a new motor when you're having trouble with all the money building up in your accounts and nothing to spend it on? If you don't have deep pockets it isn't fun. As already said above you should be prepared and capable of being your own warranty station if you want to run these mods. I'm a modder, most every car I've owned has seen headers, programming, and on and on so I'm not preaching. I'm saying think about it before you jump in.
It's been quite a few years since I did all this but I do remember a few other things. Once this happens your drivetrain can be flagged if you will, they call it different things with different brands. When that happens you have two possibilities neither of which is good. Your drivetrain warranty is voided while the warranty carries on in full effect for the rest of your car or else drivetrain repairs are on a case by case basis and the warranty carries on in full effect for the rest of the car. People often talk about having their entire warranty voided but that isn't legal in any state except for a few specific things that wont apply here. Off the top of my head you have odo tampering, the car was declared a total loss, altered so much as to completely change its intended use from one thing to another, couple others that I cant remember.
I don't know the costs here BTW, I pulled that 20k out of you know where. On my last car the DCT was 9200 parts plus installation, the engine was 25k plus installation. I don't know what the engine actually cost for one of these but I do know I wouldn't want to have to cough it up because I suspect its pretty dear.