does anyone know how to make vanilla mobs/blocks drop custom drops and how to change the vanilla recipes

if you create a loot table for a vanilla mob/block the original loot will be replaced with your custom loot table , to replace a vanilla recipe create a recipe and set it's recipe namespace to minecraft

For your Loot Table issue:
Use the Plugin Loot modifier. This allows you to add a Loot Table to an existing one without replacing it completely.

For your Vanilla Recipe Issue:
You can create a internal Datapack inside your Mod. Check this page for more help.

https://imgur.com/Ok55S9o 

You're welcome

I've been trying to add no-tree punching as a part of a new mod, but have not yet figured out how to do it.

So far, I set up a procedure that fiurst checks to see if the item stock in the hand is empty, and then checks if the target is tagged as logs, and then checks to see if the player is holding an item tagged as "axes"

If true, then it deals damage to the player and gives mining fatigue.

But the issue is that if I keep holding left click, eventually I'll mine out the log. It wont keep dealing damage.

How did others overcome this challenge?

I DO Not want to simply remove the log... or kill the player outright on his first punch.