Basically yes.
If you don't know how to modify stats you should read this primer:
http://larian.com/forums/ubbthreads.php?ubb=showflat&Number=582571#Post582571Also in there you can find templates for these files.
The guide is more for characters than skills but it's really the only guide around for this and the process is basically the same for other things like skills. So if you are starting at 0 knowledge it's as good as any place to start.
For #1
SkillData.txt (or .xlsm if you prefer to use the excel files which are easier to work in) is the file you need to work in.
In one of my mods I lowered the damage on Burning Touch
new entry "Target_BurningTouch"
type "SkillData"
data "SkillType" "Target"
data "Ability" "Offensive"
data "Element" "Fire"
data "Tier" "Novice"
data "ActionPoints" "3"
data "Cooldown" "4"
data "CooldownReduction" "50"
data "ChargeDuration" "0"
data "Damage" "3"
data "Damage Multiplier" "100"
data "Damage Range" "20"
data "DamageType" "Fire"
data "SkillProperties" "Burning,100,2"
data "TargetRadius" "3"
data "AddWeaponRange" "No"
data "DeathType" "DoT"
data "CanTargetCharacters" "Yes"
data "CanTargetItems" "Yes"
data "CanTargetTerrain" "No"
data "Magic Cost" "0"
Simply change the "data "Damage" "3" to "2" (It only goes 1-10). You can also adjust the "Damage Range" or Multiplier instead. There are formulas to figure out exactly what changing each will do, I don't bother learning it exactly though just get a feel for it by playing around with the numbers a few times.
#2 Enemy skills are usually seperate already for balance reasons.
See here is the "enemy" version of burning touch:
new entry "Target_EnemyBurningTouch"
type "SkillData"
data "SkillType" "Target"
data "Ability" "None"
data "Element" "None"
data "ActionPoints" "3"
data "Cooldown" "4"
data "CooldownReduction" "0"
data "ChargeDuration" "0"
data "Damage" "3"
data "Damage Multiplier" "100"
data "Damage Range" "10"
data "DamageType" "Fire"
Note that it has a range of 10 instead of 20 like the player version so it does less damage than the player version.
#3.
Pretty much the same ways as skills, open up weapon.xlsm/weapon.txt and modify the "damage" or "damage range". Also weapons have a "Damage Boost" section, which I'd probably leave alone until you get a feel for how the numbers work.
#4 is also basically the same as skills in that there are enemy versions of each. To figure out which weapon an enemy uses, open up the file equipment.txt (or equipment.xlsm) and see what stats entries are assigned to that character. Also you might want the editor for this so you can click enemies on the map and see what equipment entry they have.
The short version is
1. Figure out the equipment assigned to the character.
2. Open up the equipment file and find the corresponding entry (usually it's something like "Shadows_Ghoul_A"
3. On the "Shadows_Ghoul_A" list find the weapon , in this case it's called "_Shadows_Ghoul_A".
4. Open the weapon file and find "_Shadows_Ghoul_A" and change the numbers.
