hello, I hope I'm not too late. I have an idea, make fox hunt pillager just like they do with chicken, armadillo drop slime ball when brush, glow squid spawn 4 endermites on death, pig spawn an iron golem when hurt and ravangers turn into zoglin in the nether.
couldnt say it is not posible, my phone can create folder and we can use misode's github tool to make the other file. As long as we know the file structure, we can arrange them. That mean, if you make a datapack with android, it would be heck of tedious cuz no one do that but also cool as hell.
I read the changelog everytime so I dont really need the document much. But best just looking at the data folder in the .jar file. Wiki is also a fast choice for lazy people. And btw, I'm still waiting for the inventory edit upon spawning and I bet many people are too, so you're not the only one who wait.
Well didnt people already told you? You can't because it is hard code. You can only either A, B or C, move to mod/plugin. Datapack currently cant do such thing directly. There might in the near future cuz Mojang are overhauling these "hard code". You might try as well D, unpromising waiting for Mojang overhaul this so you can edit it directly.
as far as i know, loot table control which loot they give when they die, shear, etc. They dont control which in their inventory when they spawn. You can control them via datapack by give the one you replace a tag then add the loot you want to loot table using that tag