PS1 disc swap with a GameShark to play backups.. According to my foggy memory.

And how many versions support it? Nyohbuddy nyohhz..
Apologies for puke-cam. OBS gives me a neverending loop the past month when trying to load sources and still hasn't recovered from this so I strapped a GoPro to my forehead and had no idea where it was pointing during this whole thing. I'm feeling lazy just as I did while half-assed editing this crappy video of repeating myself and not focusing on what I'm talking about. So here is a synopsis portion of my post from Reddit so you don't even have to watch the video:
I remember way back when, I read some scarce rumors online about the Action Replay and a few other cheat devices that would allow playing backups but they were unattainable. Parents didn't trust online transactions and even if they did, this would spark a fear of being processed as illegal activity. I did end up getting a Gameshark and was determined to make it work. Of course, not knowing Interact was, at the time, under many guises producing these products.
Looking back, I always remember having the v2.3 (parallel port variant) with the newly included CD playing function and the ability to open some certain file types such as .str which that portion didn't prove useful as I thought it might.
A friend of mine got a CD burner and another friend let me borrow Tony Hawk's Pro Skater. Again, back then, the internet didn't have a lot of information on this that would be useful. Ripping a direct copy of a disc, even, was an accomplishment in itself. During the burn, it got corrupt. I was on a time limit to get Tony Hawk back to my other friend and it seemed like the end. I tried making another copy at a lower burn speed and it claimed to have gone a lot further, though there were failures along the way but the discs had finalized in the end so there was a closing point to the data. I ended up coughing up about $8 for wasting both of these discs.
I tried playing these on his console while I was there with his older version GameShark sticking out of the back and I had to just count it as a loss, I'd failed.
I got back home, gave my other friend his game back and was stuck with these two junk discs. Even so, it was something new that I had acquired so I figured I might as well give it a shot again. I tried many different combinations to get it to work to no avail.
Finally, I tried putting in an original, going to the music menu and pressing 'stop' realizing the disc had stopped. I swapped them at that point and went on to try to start the game. And it worked! I couldn't believe it. Especially with the data corruption, the game showed no problems EXCEPT when the level started, the music wouldn't. But if you hit start to visit the menu and then resume, it would begin playing. So the screwy data must have had something to do with the track layout.
I looked all over online and couldn't find any information about this. I felt like I had the biggest kept secret unknown to mankind. I later made a Geocities website describing the process in detail which obviously, no one would have ever visited. But I felt I did a duty in putting it out there.
I mentioned version 2.3 because I may have misremembered, after repurchasing a GameShark a few years ago to replicate the process and it didn't work. I later bought a 2.0 and couldn't get it to work on there either. At this point I sourced out GameShark images and found that UniRom was a thing. My intention was to burn a few different images to the chip to determine specifically which version I had back then. I suppose I must have got sidetracked with something else along the way. The versions I did try would reboot the game from the boot up sequence when you went to launch the game. Back then, it would skip all of that and load from the initial intro data (FMV, title screen).
TL;DR, Versions 2.0 - 2.42 will all unlock the drive for disc swaps. Provided your laser is in good, working condition. As for the GameShark Pro 3.0 and onward; I don't have an answer for those because I don't own one and the flash is just a smidge bigger than the onboard eeprom provided in the 2.0 I have here..