To what extent can you modify the game engine?

[EggPooPoo]

I'm not referring to with "Triggers" I suppose, but to what extent can you modify the game?

I have some cool ideas like where you can have a unit or hero run up to the water when you right click the water, and he can dive into the water when he gets close enough!

Currently, if you set his or her/it's movement type to being able to walk on water or whatever, what will happen is it just keeps doing it's walk animation or a possible swim animation into the water. I want to mod the engine so that there's an ADDITIONAL animation to every model; one that will play when the unit is about to get into the water! So you can have like Stand 1, Stand 2, Walk 1, Walk 2, Swim 1, Swim 2, then Dive 1, Dive 2, Dive 3! Other ones to allow him to dive underwater, I think they already have Submerge 1, but this ties into another concept!

I want to try to mod the water engine, so you can create some dynamic water effects with physics programming and get units to be able to swim underwater! Perhaps it would be part of a map with a keyboard system where you control units with the keyboard instead.

So is it possible?

 

[Lizreu]

Theoretically possible on version 1.26 with Memory Hack and other tools. There's quite a lot of documentation on the topic, I believe, you only have to dig around a lot.
However, WC3 was not meant to be modded beyond what is offered to you in the JASS API, and doing any kind of extensive revamps would require very good reverse engineer skills, tinkering with assembly, debuggers, and all the other nasty stuff.

Other than that, no, not really. Stick to well-established, modern engines like Unity or UE4. It will be easier than trying to coerce a 16-year old engine to do what you want.