I took a stab at the Shadow Step skill for Enhanced Edition, and was semi-successful...
The animation didn't work (the character just raised their dagger and everything was hit simultaneously), but it did backstab all targets in range.
From what I can recall from when I made skills in Classic edition, you can't change the pre-existing skills directly. Instead you need to create a new skill with the modified parameters and change all references from the old skill to the new.
Here's my Skilldata entry:
new entry "CHANGED_ShadowStep"
type "SkillData"
data "SkillType" "Shout"
data "Ability" "None"
data "Element" "None"
data "Requirement" "DaggerWeapon"
data "ActionPoints" "8"
data "Cooldown" "8"
data "CooldownReduction" "20"
data "ChargeDuration" "0"
data "Damage Multiplier" "250"
data "DamageType" "Piercing"
data "SkillProperties" "AlwaysBackstab;Bleeding,120,3"
data "CanTargetCharacters" "Yes"
data "CanTargetItems" "No"
data "CanTargetTerrain" "No"
data "Magic Cost" "1"
data "TargetConditions" "Enemy"
data "UseCharacterStats" "Yes"
data "UseWeaponDamage" "Yes"
data "AreaRadius" "8"
data "Icon" "Skill_Rogue_ShadowStep"
data "DisplayName" "Target_ShadowStep_DisplayName"
data "DisplayNameRef" "Shadow Step"
data "Description" "Target_ShadowStep_Description"
data "DescriptionRef" "Step through the shadows and attack surrounding enemies from behind, dealing [2] weapon damage. Then go back to where you came from."
data "StatsDescription" "Target_ShadowStep_StatsDescription"
data "StatsDescriptionRef" "Range: [1]<br>Damage dealt depends on your weapon's damage rating."
data "StatsDescriptionParams" "TargetRadius;Damage"
data "FXScale" "100"
data "PrepareAnimationInit" "skill_shadowstrike_start"
data "PrepareAnimationLoop" "skill_shadowstrike_loop"
data "PrepareEffect" "FX_Skills_Rogue_ShadowStrike_Prepare_A"
data "CastAnimation" "skill_shadowstrike_cast"
data "CastTextEvent" "cast"
data "CastEffect" "FX_Skills_Rogue_ShadowStrike_Cast_A"
data "TargetCastEffect" "FX_Skills_Rogue_ShadowStrike_Impact_Male_A"
new entry "CHANGED_ShadowStep_1"
type "SkillData"
using "CHANGED_ShadowStep"
data "Level" "1"
For debugging purposes, it's important to make your skill low-level until you get it working correctly. Thus I removed the "Tier" data point and changed the "Ability" field to "None", so that it won't be removed due to insufficient skill points. You can change the requirements later once the skill works properly.
I also had this story script to give the skill at the start for me to test:
IF
DB_CYSDoTutorial(_)
THEN
CharacterAddSkill(CHARACTER_Player1, "CHANGED_ShadowStep");
PartyAddGold(CHARACTER_Player1,1000);
The 1000 gold is just to check that the skill should have been added.
For more information on changing skills, it might be helpful to take a look at my stickied topic "Main Campaign Modding" (specifically the "Adding new skills/items to the game" in the first post). Although the thread was made for Classic edition, a lot of the information still works for Enhanced Edition modding.