Using passengers and other command witchcraft,
passive mobs are made hostile.
This will run upon opening the world with no annoying welcome message.
This pack works on 1.18 and while it theoretically may work on earlier versions, it's untested.

List of all affected mobs=>
-sheep
-cow
-chicken
-pig
-horse
-axolotl
-iron golems
-spiders/ cave spiders (during day)
-wolves
-bees
-bats
-llamas
-pufferfish

If you want to disable the pack,
use /datapack disable followed by the pack name
then use
/schedule clear angy:second
/schedule clear angy:minute

Any problems leave a comment and I will get back to as soon as I can.