[Dr. Jekyll and Mr. Hyde]

Use Wrye Morph. Does exactly that.

[Destroy Dark Brotherhood! <3]

I actually wanted something like this myself, only I was thinking more along the lines of pointing the Imperial Legion to them and letting them take care of it. I also wanted to steal Shadowmere. Because that would be funny. And I can. :tongue:

 

If all you want to do is kill them, why not just join them and use the Kill a Night Mother mod? Don't feel like playing a spy?

[Fingergun Spell casting animation]

A mod called Spell Singer already has an animation like this. It's very girly though, so might be out of place on male characters.

[Huge dog transformation.]

You might want to keep an eye out on the Druid mod 2.0. It's not been released yet, but the rewrite includes wolf transformations with bigger wolves.

["Proper" khajit and argonian bodyshapes/animations]

The meshes aren't bad though they do seem to have a couple of solely aesthetic issues. The biggest one would be making the calves shorter. I personally think it looks really awkward, and it's likely going to make it a pain in the butt to get the feet to work with any type of unmodified pants. I don't suppose the Real High Heels mod would help with that, would it?

 

Second thing may just be me being picky. The toes seem to have some odd lengths there. Were you going for a more human-like foot? The toes on a cat paw don't shorten to the outside like that. The middle two toes are roughly the same length while the outer two are slightly shorter, as you can see in this picture.

[Owned horses stay put]

Been done:

Call Mount - Stable Master

[Meshes, textures, spells]

Edit: Actually, you know what, forget the rest of it. I'd be happy enough with just the Khajiit teeth and tail.

 

I want a Khajiit that looks like this. To do that I'll need a short, fluffy tail and a tooth mesh. Preferably the teeth would use Scanti's Merged Teeth as a base, as I happen to like having whiskers on my kitties.