Have not really seen this discussed anywhere, so maybe this might help some people out. The Swap trick does indeed work mid game. Some games don’t allow you to save on disc 1, and then boot disc 2 and continue. Parasite Eve for example, makes you insert disc 2 while playing disc 1. There is no workaround to doing this. Lots of people will tell you that you just won’t be able to play these games without a mod chip. Well, that’s not actually true.
When you get to the Insert Disc 2 screen, swap in a legit PSX game. Unblock the lid sensor so the PlayStation thinks the cover was open, and then block the lid sensor again (I use an aluminum foil rod I shaped for this). The disc will start spinning fast (2x speed). As soon as you see this happen, swap the legit PSX disc with your CD-R of Disc 2. Worked for me even on a SCPH 5501, which usually requires a double swap trick at boot. Now that I have an October 1995 SCPH 1001 and use the audio menu swap trick to boot games this is the only ‘live’ swap needed to play Parasite Eve for me.
I do have to turn the console to the left vertically for it to read CD-Rs (legit games read fine normally) but that’s just my specific console.
Hope this helps someone out!