Wow, I didn't expect such a fast reply, let alone from 3 different people! I was afraid this place might be dead, I'm very happy to be proven wrong!
SyperSzym: That's gotta be right: Soldiers and Combat Droids gain the same amount (the HK-47/Mandalore/Handmaiden example), so there must be a connection. But that's not the point. The point is: how do I modify these amounts?
Goat: I'm aware of that, but like I said, I'm editing the utc files using the K-GFF editor. I'm not editing save files with KSE. Believe me, I've already tried that...
HOWEVER... I must report that the HP can actually be changed through the KSE, but the problem is that: 1) It only works when it wants to and 2) You have no control over the final amount of HP of your character.
Let me explain myself: I once tried to change HK's HP during a walkthrough, just as I had made it in the HK factory. I think HK's current HP was something like 890 points and I wanted to cut it down a bit. So I used the KSE and changed the HP value to 0. After I loaded that save, I noticed that HK's max health had decreased to 860-something. It was nowhere near the amount I wanted, but it was a sign of progress, so I kept decreasing the HP in the KSE. Unfortunately, HK's health in the game would not go down anymore, even though I had started using negative values in KSE. I finally gave up at the point when I set HK's value in KSE to a 8 digit negative number in a desperate attempt to bring HK's health down, only for the HP to increase to a monstrous amount of 11000 HP.
That was a little boring and off-topic, I know, but it shows that a character's HP can be edited through KSE, except you can't set it to the amount you desire and it also doesn't work 99.9% of the time.
But again, I'm not editing the save files, Im editing the utc's, so none of that really matters. I can control how much HP each party member has when they join, I'm just looking for a way to edit the amount of HP they earn per level up. But I guess you already know that.
And finally, Fair Strides:
The "hitdie" column? Didn't cross my mind-I examined the classes.2da file but didn't really pay that much attention to that specific column, I thought it has nothing to do with it. But now that I think of it, it might be exactly what I'm looking for: The column that determines the HP earned per level up should be tied to the classes file! Let me check that out and I'll get back to you.
Oh, did I say "thank you"? No? Here, let me say a big "THANK YOU" for bothering with a noob like me... Thanks to SS and Goat for their feedback as well! Cheers! xD