If you have some programming knowledge, here a reference: https://github.com/LiveSplit/LiveSplit/blob/master/Documentation/Auto-Splitters.md

Ah okay. Auto-splitters have to be made for specific games in order to work. It monitors memory values to know when to initiate a commands. If you wanted to make one yourself, I'd suggest getting a program like Cheat Engine to help find the hook for the memory values, which you then add to the autosplitter.

For specifics, Cryze and Wooferzfg can help.

It's not COMPLETELY different each time you make one; you'll generally go through the same process.

You can find a hook by using Cheat Engine's ability to watch memory. You continuously test to find a certain value (like, say, money value) until you nail down where the value is being stored in the memory. How exactly you then get the hook I can't recall, unfortunately, it's been a while and I'm not properly equipped to check.

Sure, you'd be checking when you do and do not have the achievement/item. It may take some time if it's a Boolean value.

I really would, but my predicament doesn't let me.

Asking the Developer where it is, is useless. They don't know either (usually) since the Engine/Game/OS handles that and the dev doesn't have to say at which point he want's to store stuff.