That might be tricky
For field models:
1. Open Deling (editor)
2. Select field you want to modify
3. Click on 'Script' tab
4. Select character you want to modify (e.g. Squall)
5. Click on script label with no name
6. On your right you will see "SETMODEL XYZ"
7. Change XYZ to number ID of model you want (You can see the lists of models in '3D Model' section, first entry on list is ID 0, next entry is 1 and etc...)
8. Click on compile on bottom right
9. Click on 'save' icon
You can also grab other chara.one file and put it in the field archive to use models from other fields (except exceptions, if some entity use model ID higher than model count)
In the video, you can see Rinoa's father at 7:54. 100% author took the Deling chara.one file and put it there
For battle models- there was a PSOne code to change the party to given monster ID. Author in this video claims to work only on file manipulation. I don't believe casual renaming files could work here
EDIT:
WHAT THE
https://www.youtube.com/watch?v=0UAns5WgzRw&list=PL40B4F9F24139705D&index=1
Wow, I can not believe you answered me. No more than a few hours ago I subscribed to your channel when I was watching this video:
https://www.youtube.com/watch?v=hf4m5S-VpXw&t=14sThats really insane, you managed to change the animations of the spells in the PC version, which is no small thing.
Regarding to change the battle models, you refer to the codes of King Edgar 0's (
https://www.gamefaqs.com/ps/197343-final-fantasy-viii/faqs/4940), however, in the video the user Is not using the PSX version, rather, it is from PC. And I mention it because Fujin & Rajin can not use the "attack" command (in the PSX version), since that crash the game.
So the person behind the video replace not only the battle models, but also the menu commands with monster / enemies skills. Almost 20 years have passed since the original release of the game, and running into these things drives me crazy. That is why I would like to offer any help needed by the people who make up the FF8 team to achieve that kind of progress.