Apparently, I've searched all the internet for something like this. At this moment I have NO IDEA why I was not able to find an answer.

So.. I just found out myself. Ever wanted to change Career Salaries or Work Hours?

Let's get straight to the point:
- You'll need Sims4Studio. Simple as that
- Tools>Create Empty Package
- Choose a name and hit Save
- Tools>Extract Tuning
- Fill in the search bar with whatever your heart desires to change in the following form:

* If you want a Teen Career: "career_level/career_Teen_<Career>_Level<Level>" Where you replace <Career> with the Career Name and <Level> with the corresponding step in the Career (for Teens, from 1 to 3)
** Example "career_level/career_Teen_Barista_Level3"
* If you want an Adult Career: "career_level/career_<Career>_Level<Level>" Where you replace <Career> with the Career Name and <Level> with the corresponding step in the Career (for Adults, from 1 to 10)
** Example "career_level/career_Astronaut_Level7"
*** KEEP IN MIND that some Adult Careers have BRANCHES. If you take a loot at the Astronaut Career, you can see that it stops at Level 7, then it has different entries for both Branches "career_level/career_Astronaut_Ranger_Level<Level>" and "career_level/career_Astronaut_Smuggler_Level<Level>", <Level> ranging from 1 to 3.
**** I suggest you simply type "career_level/career_" then have a look at everything it offers (You'll see that you can also change School and High School entries)

- After selecting an entry, hit Add To Current Package. Afterwards you can just close the Extract Tuning window.
- Left side, in the "Type" column select the first entry.
- Now you'll find yourself with a huge code sitting in your face. This is your playground. Above the code there are two tabs "XML" and "Data". Make sure you are in the XML tab.
- Navigate to the very bottom of the code. This is the stuff you'll most probably want to change.

* YOU'LL SEE SOME STRINGS SIMILAR TO THIS

<T n="1 MONDAY">True</T>
<T n="2 TUESDAY">True</T>
<T n="3 WEDNESDAY">False</T>
<T n="4 THURSDAY">False</T>
<T n="5 FRIDAY">True</T>

* Above is the weekly schedule. Change True to False and False to True depending on what schedule you want to have. Set True for Work Day. Set False for Off Day.

<T n="duration">5</T>
<U n="start_time">
<T n="hour">10</T>
</U>

* Above you can change the duration of the shift (in hours) starting from the "start_time" value, which is the hour of the day your Shift will start. In this example, my Shift starts at 10:00 (AM) and ends at 15:00 (PM).

<T n="simoleons_per_hour">516</T>

* You'll see many strings related to "CareerTone". Look VERY CAREFULLY ABOVE THOSE until you find the string above. This is, obviously, the amount your Sim will win per hour. Change this to whatever your heart desires.

<U n="wakeup_time">
<T n="hour">8</T>
<T n="minute">0</T>
</U>

* I haven't really tested the one above, which I suppose is some kind of Alarm Clock for your Sim to prevent them from Sleeping too much and giving you around 2 hours to prepare for work.

- After you are done, simply click SAVE in the bottom-right corner. Right now you can close your Sims4Studio
- Almost ready, just navigate to your saved .package file, copy it, and paste it into your Mods folder.
- BOOM. You are ready to go!

* If you want to change multiple Career Levels just repeat the steps involving Adding from Extract Tuning and Code Editing. Add as many entries as you want and when you have changed everything that you want, click SAVE and move it to your Mods folder as a compact, single .package file

I am not really sure if it's the right category or if someone cares enough to read this. I am happy if I at least have this tutorial to use it later on. Thanks for your attention.

This worked wonders. I just pray that EA doesn't rejigger things on me lol. changed school hours and the chief justice one.