An interesting topic that deserves it's own thread.
As soon as you change the rubbers or globes on a pinball, it is not "factory original".
My thoughts are that for a Hobbyist, there is no issue in transforming a lesser title into an MM. This is a cheaper way of owner a reasonable title that is set at an inflated price. There's a lot of work that needs to be done and I follow Robm's thread with interest.
If a business sells a re-badged MM as a "High End Restoration" and fails to disclose that it is not original, then that's a problem on both fronts.
Using the Funhouse analogy, it is and was always a Funhouse. You can trace the Serial numbers back and it was always a Funhouse. You can change almost everything, and it is still a Funhouse. You can sell it as a "Restored" Funhouse.
Using a NBA Fastbreak or Congo and converting it to an MM is not a "restoration". The serial numbers will always be Congo or NBA Fastbreak. When it is sold, it is not a "High End Restoration" or an "original" MM. As long as the business highlights that it is NOT original, I have no issue with the process. But I find it ironic that the inflated prices set by resellers for this title has created a market for the conversions. I'd be interested to know what the price is for one of these. I'd expect it would be far less than an original. That is, assuming the customer is aware it is not original.