You can do pretty much whatever you want as long as it's for personal use only. Copyright troubles enter the picture as soon as you release art, voices, sounds, designs, etc without permission of the copyright owner.

However--some organizations/individuals turn a blind eye to fan-made content so long as it is for non-commercial/free use.

Like I alluded to in an earlier post, movie franchise owners tend to be a bit more forgiving with freely distributed fan-made content--it's a kind of wink-and-nod arrangement. Pinball companies, on the other hand, are incredibly strict about copyright and licensing. Granted, there is a difference between content (movie characters and stories) and goods (pinball parts).

That's a repair service, rather than a product purchase.

The ROM software is freely accessible for Bally/Williams/DE machines, so there's no problem with ROMs there. Gottlieb is a bit different where their ROMs need to originate from an authorized reseller since they have not been publicly released.