Rentarou

You can use this to add a new key binding, but you'll have to dig through the source files yourself to find where the aiming code is located. I'd probably start with the Character classes. You can use JD-GUI to easily search through the source and look for keywords.
A warning though: If the aiming code is handled on the Java and not on the Lua side, it will be hard(er) to mod it, because you'll have to decompile, mod and recompile the necessary files (and the mod will constantly break with new versions of PZ).

No need to be sorry, after all that's what the Help forum is for

Yes, should be do-able.

Right now combat is knock-down zombie and keep pressing left click till it is dead.
That's both time and durability consuming.
 
I suggest pressing E near a knocked down zombie would make the player instantly kill it, the process could take a while so using it when fighting a group isn't an option but suicide.
 
Also, reduce the chance of zombie falling down when attacked and instead make an animation or they staggered with a higher chance of falling when hit back.

Right now combat is knock-down zombie and keep pressing left click till it is dead.
That's both time and durability consuming.
 
I suggest pressing E near a knocked down zombie would make the player instantly kill it, the process could take a while so using it when fighting a group isn't an option but suicide.
 
Also, reduce the chance of zombie falling down when attacked and instead make an animation or they staggered with a higher chance of falling when hit back.

I support this.

It does seem a little redundant to need to unlock a skill with xp then purchase it with the xp you already earned.
 
In my opinion, the skills should automatically increase when you get them high enough, and the 'global ex' (that you earn for doing anything) should either be removed. Or, if you don't want to remove it, have it be spent on something else, like increasing base attributes. (I think there's only strength and fitness right now, but i assume more could be added. e.g. a perception skill that modifies your vision radius.)