In theory Moss-Mag "prove it" is true, in practice it's complete crap, here's why:
(1.) The MM wasn't written to protect modders, it was written to protect to average consumers trying to repair their cars; protect them from, say, GM requiring that consumers could only repair their cars with certified GM parts ...
and judges know this <- important More on this in a sec ...
(2.) There's not really a legal thing of "voiding a warranty" (except in very specific explicit circumstances) - what actually happens is an independent business called a dealer submits a request for reimbursement for warranty service from BMWNA and BMWNA either reimburses the dealer ..., or not. Typically for big repairs the dealer will get pre-authorization for work. If BMWNA suspects you've violated the terms of the warranty (by modding), they'll simply deny to reimburse the dealer for the service cost (or deny the pre-auth), which mean either you pay or the work doesn't get done.
(3.) BMWNA can deny warranty work at any time for any reason ... or no reason. BMWNA requires approval from no one - they can deny work any time they want and the consumer's recourse is to sue .. and in court the consumer can bring up an ole thing they want, including Moss-Mag, but that's probably a bad idea (see judges)
(4.) If a consumer sues, that court date is years away because BMWNA's lawyers will delay the trial via continuances for as long as possible; since the car is evidence, it'll have to sit idle during those years of continuances. BMWNA has plenty of time. You probably don't.
(5.) BMWNA also has lots of experts on your car - they built it! BMWNA has all the data, all the engineers, all the design, and all of the knowledge. They'll bring all of that to court with them ... years later. What do you have? nothin. you can hire expert witnesses, but if you don't win you lose those fees.
So, at the end of the day, using Moss-Mag in court assumes you get through the 3-4 years it'll take to even get in front of judge. Then that judge - who's not so excited to hear about why you believe your modding fuck-ups should be funded by BMWNA - will hear from BMWNA's 50 expert witnesses and then he or she will hear you.
Spoiler alert: that's not gonna be a good day in court
A few selections from the X5 warranty:What is not covered:
Modification of the vehicle or installation of any performance accessories or components attached to the vehicle which alters the original engineering and/or operating specifications or which results in damage to the other original components, electrical interference, electrical short, radio static, water leaks and wind noise.
Here's where BMW gives a shout-out to Moss-Mag in their warranty languageNon‑genuine BMW Parts — While you may elect to use non‑genuine BMW parts for maintenance or repair services, BMW NA is not obligated to pay for
repairs of the non‑genuine BMW parts or for repairs of any damage resulting from the use of non-genuine parts.
This warranty does not cover malfunctions caused by any of the following:
accident, flood, misuse, modification, alteration, tampering, disconnection, improper or inadequate maintenance, except if performed by an authorized BMW center doing warranty repair work, use of leaded fuel or fuel other than as specified in the Owner’s Manual.
So, basically, yes, hardwiring could have warranty implications because it's "modification, alteration, tampering, & disconnection".
If you want to be ultra-safe, then using cigarette lighter sockets for power would be the way to go ... once you start jamming stuff into fuse blocks, clipping onto wires, etc technically you're risking paying for anything that blows up with your electronics.