May I double the exp needed for each ship and just give them 2 skill points each lvl? I can just change 1 file for it or I have to do all the cap ship and titan files? that is about 27 files we are talking about here
You can't have them give 2 skill points per level. Capitalships always get 1 and titans two. All you can do is double the XP and double the stat bonuses ship get on level up as well as double the effect of the abilities (make them twice as powerful, or however you want to scale it).
Basically you can't change how the fundamental level up system works, just the precise benefits the system gives on a capitalship/titan basis. 1 file to change the XP, lots to buff all the needed ships.
thats funny, can I combine skills then?(like put them in a spell book) i.e. I can combine the defence passive(of which I don't think anyone will not max it for their titans) with the weapon passive(which I don't think many titan really use it) so that I can free 1 slot?
Sure, but for capitalships that still uses up an ability slot for the passive. In fact for passives you can cram as many effects as you want basically.
I should also mention the 5th ability slot is highly limited on capitalships, since the skill selection button is in the 5th slot so it can only be used for passives or abilities you only want to be autocast for some reason. Players cannot manually use the 5th ability on caps/titans/starbases.
Or can I make a skill acts like manage icon(the one you use to set the Engagement area and fleet thing) so when I click it it opens up another page and can choose/use skills from there?(basically a spell book)
Nope. Again lots of mods would love to do that if it were possible. You might want to play some to get an idea of just what they change (and what they don't).
I do see the entity files but I don't know if the tutorial did tell me all entity can be modded or any of them I should leave it untouched. and mentioned a converter for the entity files but I can't find the download since the most entity files can't be read by notepad
You can mod them all if you wanted, or even make your own entity files for say new ships.
The basic converter is technically always kept up to date in your Rebellion installation folder.
We had better guides but the websites they were on no longer exist (and the search feature on these forums isn't very good). There's probably better ones but this is the official tutorial from the devs (you can get it in a more readable pdf if you download the tutorials in the forge tools from the download section of this site, but everything but the pdfs are way obsolete). It's old but mostly still true for entity files.
Here's all the vanilla files already converted for rebellion. 1.82 (AKA the reference data) if you don't like command line tools. Harpo also has a GUI tool you can try, but I don't use it myself.
Why they don't make the entity files as txt at the first place? does it speeds up the game or something? Whats the point to make them entity files if we gonna make them txt anyway?
Yes, and reduces the game's file size (AKA downloads faster). The game can run them in binary or txt format though, so you never have to convert them back if you don't want them. 99% of people don't even try to mod the game themselves, so why not make things a bit faster for them?
I mean there are really just too much files, I know its a good way to keep the Mod running if only one file is broken (which should be a must have idea for all mod friendly games) but lack of a basic search engine or guide even just put them in sorted group folders, make modding the game really hard for green horns like me, Im not even sure where to start!
Hey, my mod Star Wars Interregnum and its core, the Enhanced 4X mod, have more entity files than the base game, and the vanilla files are loaded too! 
Every type of entity file has a prefix though (Capitalship, Frigate, Planet etc.) that tells you what they are. While they all have a .entity extension, each type of entity has its own fixed format (so you can just say copy planet population numbers from a planet and put them on a starbase to get starbases to generate credits). Once you learn the naming convention, its not hard to find what you're looking for.
Thanks I will do that, does this effect any saved game though? I got few unfinished games.
Changing game files mid save game is generally a bad idea. If you change numbers like a ships' health, that usually works. Other changes might not work until a new game, or in extreme cases they might break the save game.
You are creating a mod in your mod folder to mess around with right? NEVER CHANGE THE BASE GAME FILES. Make everything as an official mod, so you can just disable the mod from the options to go back to vanilla and play your save games/multiplayer without issues.
thanks, does those file the same location with stares or they got other folder? and for adding researches where should I put the icons ,they do need one right? I don't want my research end up a question mark in the game....that would be silly
GameInfo basically has all the files used for actual game numbers. Textures contains all the image files. Brushes files in the Window folder tell the game where in the texture file an icon is. Sins can use .dds or .tga images. Paint.net is a good free image editor that can save both natively if you don't know much about image editting.
I would just focus on getting the research in game first before worry about art assets. 
You can just copy an existing research and it will use that research's icon until you change it. Oh and any text you want in game goes in the String file in the String folder.
Finally, if you add any totally new entity files, like research, make sure you add your new research entity file to the entity.manifest file, otherwise the game won't load it.
thank, oh btw doest mod disable achievements? I got 5 of them left
No, but obviously if your mod say disables the Advent, you can't get any advent achievements while playing it.
which file indicate the lvl cap for AI can buy? what about titans? I would love to see a high lvl titans when they come out at late game (but not early though, that will be annoying)
Titans by default keep their levels on death, so if the AI ever gets a high level titan, they'll keep it everytime they rebuild it.
Sadly we can't directly edit the AI benefits (psychoak mentions the hack we use to make our own AI only benefits). But its fairly substantial on unfair and harder AI. They can easily get 6+ level capitalships if they have the credits.
