Sorry for the extreme delay in replying, I got caught up at work with a few important things.
So what you will need is a database browser I recommend DB Browser for SQLite: https://sqlitebrowser.org/
Then you need to go to the game's files and extract the definitons.db from the commons.jar archive. That is found inside the archive under commons/definitions/definitions.db
Then you need to open the definitions.db with the DB Browser and navigate to the table named Npcs.
There find the animals you want to change the behaviour of and set the behaviour field from AGGRESSIVE to DEFAULT.
Then save the changes via the "Write Changes" button and repack the definitions.db to replace the other one in the commons.jar archive
If you have any more questions feel free to let me know