This topic has been discussed lots of times through the years. A quick search in this forum should give dozens of thread entries. Check this thread for instance
https://www.psx-place.com/threads/i-cant-play-psx-pal-games-on-my-ps3.18264/
Iirc there is no ideal option & you might be better off getting a new copy of the game in the video mode you need.
However I am not the best person to get advice from, my TV supports all modes, I never play ps1 games from another region on my ps3, you may prefer to wait for recommendations from people who regularly use/used ps1 games from various regions & experienced the same issue as you.
1. A CD image can be patched (converted ntsc/pal with tools like PAL4U) but I don't think it will be enough to run properly. You may need to change the hdmi settings manually once the game is mounted or possibly swap the xRegistry.sys with a version that uses the right /setting/display settings.
FYI if you find some registry settings helping with your problem, note that swapping the xregistry.sys file can potentially be done automatically at the press of pad button or XMB icon if you wish to set that kind of thing up.
2. You could patch the CD image (to convert the video mode) then transform the patched image into a ps1 classics game & modify the param.sfo to use 480p.
In theory this method should work fine.
3. You should use cue/bin format rather than iso for ps1 backups. Afaik the cue sheets are essential in many cases..
4. I don't think you can get the original CD to work OK even if you fake the region & choose the right video output settings in the xRegistry.sys. You can try I suppose, all registry settings (including region & display settings) are listed in the wiki.
https://www.psdevwiki.com/ps3/XRegistry.sys
The xRegistry.sys file can be found in /dev_flash2/etc. You can transfer it to your PC, use xRegistry.sys Editor 0.75 by stoker25 to modify it & overwrite the file with your modded version in /dev_flash2/etc. Remember to keep a backup of the original file & keep in mind that the Registry is an essential part of the system, the system always keeps its own backup but still, file corruption may lead to problems & potentially internal hdd reformatting.