First things first...
Find out exactly which plcc chip that's in there...because even if you have the hex code you will still need to physically program it...
I doubt that it's an eprom though, much more likely to be a prom, or even a small micro, but will most likely be a burn once only chip. However, it may be replaceable with an nvram, eprom or flash micro part etc.
If you plan on testing tweaks and stuff with this, it may be better for you to make an emulator and pod, rather than constantly pulling chips, but if you're gonna just use a chip, at least buy yourself a cheap plcc puller as opposed to using a needle to lever it out unevenly, it will save you damaging the chip and socket. If it's just a prom, he's talkin rubbish about it being a locked anything, hex is hex...however he may mean that once the chip is installed, the management system personalises it, and it can no longer be used in a different system...so if you buy the chip from him, make sure you make a back-up copy of the hex first. If on the other hand, it's actually a small micro, it may well have the memory locked.
Start off by figuring out which chip you need, and then you'll have a better idea what to build for programming/emulation etc
Oh, just a side note, most of these things are set-up and stored from physically running the car/engine set-up on a rolling road or dyno, so your car may not have the same performance because of variation in sensors, engine wear, emission system etc etc
You may in actual fact end up with something that runs poorer than what you have now...