It is theoretically possible to extract the code and work on it - look at what's been achieved by Pinball Browser in allowing you to change sounds/images.

I've worked on several projects over the years where we had to take compiled machine code and work stuff out to change what it does and it is incredibly difficult. The number of inputs and outputs on Pinball just multiply that complexity.

For example, at first you'll need to identify how every physical device is addressed and where and I'll bet that this isn't all done in a single place for Switch #33, it'll be in loads of different places. To make a simple change may not be too bad - eg recoding so that hitting a pop-bumper gives 2000 points instead of 1000 would be doable, but to try to implement complex rule set changes just isn't feasible without a huge amount of effort and that's required for every single game individually.

Doing that requires physical access to the machine and I just can't see enough people with sufficient low-level skills (very few current day programmers have even seen machine code or worked with it let alone spent time reverse-engineering it!) putting the amount of time in that is needed.

Unless source code is made available, then it really isn't going to happen.