Sorry to resurrect an old thread from the very very dead, but... I just discovered in all this old Williams archive stuff that I got from Steve Kordek and elsewhere, that Paul Dussault actually created a version of Flash with lane change, in December of 1982. Not sure why. I'll ask him next time I talk to him. Looks like he wired the switch (presumably on the flipper assemblies, a la Firepower) to switch #47 in the matrix. It's coded to work with Green Label ROMs (most Flashes were Yellow Label originally) and will show up as "1486 9" in the self test. If anyone wants to try that out, I'll try to develop a proper binary file for it (not straightforward).

OK, as promised here is the "version 9" Flash Game ROM that adds lane change:

http://backglass.org/williams/kordek_archives/flashv9.2716

This requires Green Label ROMs. You'll need to add a switch matrix switch to the right flipper assembly - normally open, with a follower nub so the EOS switch will push this switch closed when the flipper is up (exactly like it's done on Firepower.) Don't do this if you don't know what you're doing, as putting flipper voltage through your switch matrix is an especially bad idea. Move the wires from the nearby playfield tilt switch (the one with the big weight on the end of the blade) to this new switch, and you're done.

The person I had test this out for me described the result as "underwhelming." No doubt. Lane change was a really big deal when it was invented, but it's gotten a lot more interesting than it was back in those days - one direction only, no special sounds when it happens, etc.