So I was reading the thread started by BIO about EUP's, and extending beyond that of a unit death. I was wondering, how can I achieve this. The thread itself was a little confusing to myself. What programs do I need, what do I have to modify, is it all still a regular trigger? Do I need to change a certain vespene gas ID? Can somebody give me some beginners pointer tutorial how to transform a ghost to shoot wraiths without dropping? Thanks a bunch.

So I did some testing. I see that it's a unit being placed at a certain Index ID, Player, and Unit ID. My question now is, how do you exactly kill this vespene gas? Because it doesn't auto shoot it down.

Welcome to Sen, supermangik, and welcome to the world of extended units.

You're asking a lot of questions on a topic that hasn't been fully developed; we understand the mechanics of EUPs, but we don't know very many extended units that work for them. If this is a path you're interested in taking, you should keep in mind that a lot of the work will probably fall on you to understand and solve on your own, which is going to take a bit of time, especially if you're not very familiar with EUDs in general. An excellent starting point would be reading http://www.staredit.net/topic/14226/.

Regarding EUPs, the http://www.staredit.net/topic/15356/ thread is the only real source of documentation we have at the moment. As for your questions:
There's a lot of rough information in the thread, but you may find the following posts from it helpful:

http://www.staredit.net/334563/
http://www.staredit.net/334741/
http://www.staredit.net/336010/
http://www.staredit.net/336082/
http://www.staredit.net/340685/

And of course you can check the wiki created for documenting information on EUPs: http://neoeud.wikia.com/wiki/SCBW:_NeoEUD_Reference_Wiki

You'll need a good map editor, such as ScmDraft 2. That's the only program you need to use, but if you don't want to do calculations by hand, you can use http://www.staredit.net/topic/15378/ to calculate the necessary unit/player ID combination to affect a particular address.

And no, these are not triggers. You are placing a unit on the map.

The original unit you change does not matter; as you're changing the unit's type ID, it is no longer a Vespene Tank or whatever unit you chose to initially place. It's an extended unit: something that doesn't intentionally exist in SC. It's like someone asking "What's your favorite color?" and you giving the answer "Potato"; the result isn't a color, though we could interpret it to be brown based on the color potatoes are. SC does the same thing, where it may interpret the extended unit to have the sprite of a Protoss Gateway, for example.

So yes, you need to change the Unit Type ID to turn it into an extended unit. You'll also need to change the Player ID based on which address you're trying to change.

Again I'll refer you to the EUD tutorial, particularly Section 6, which covers unit EUDs. It describes how to find an index ID, and how to find a particular property for the unit on a particular index.

For turning a Ghost into a Wraith, you'll need to change the Ghost's unit type ID from 1 to 8, which means you'll need to preplace 7 extended units targeting the Ghost's unit type address. You can find the address manually and then plug it into EUPCalc to see possible UnitID/PlayerID combinations to assign to the preplaced units (warning: most combinations will cause SC to crash), or you can go through the Theories topic and take one of the existing example maps that are changing one unit to another and just copy/paste the extended unit located there (after placing your Ghost at the correct index ID).

The hitboxes on these extended units (which aren't actually "Vespene gas" unit types) are kind of weird. You'll have to place the unit to kill it far off to the left (see some example maps in the Theories topic) for the unit to automatically attack it.

Hey Roy, thanks a bunch for taking your time to answer my questions, really appreciate it. BTW, is there a list of combinations that works and that doesn't work? It'll be great if everybody posted what they have tried, and haven't.

there's a few lists of combos that do work in the theory thread, i've cooked up a program that can identify units that don't crash the map (though they don't check if it can be killed or given -- yet, I have been working on it a bit lately), the link to which is inconviently located: here

some lists of that programs output can be found here: http://www.staredit.net/topic/15822/