For Newbie: "If u want edit\decreases OP skill's"
First u must know name or id skill,if u dont know name:
Alt + g in game u must write skill name and click search, if u write good name skill u must get id that skill
Example:
Shield Slam has big chance and a lot duration time[id Shield Slam is 353], we must go to [this is my files location, u can have other] - C:\l2j\gameserver\data\stats\skills and open 0300-0399.xml
U must search it
<skill id="353" levels="1" name="Shield Slam">
<set name="magicLvl" val="77"/>
<set name="weaponsAllowed" val="2"/> <!-- Shield -->
<set name="lvlDepend" val="1"/>
<set name="power" val="40"/> <!-- Base Land Rate -->
<set name="mpConsume" val="35"/>
<set name="target" val="TARGET_ONE"/>
<set name="skillType" val="MUTE"/>
<set name="operateType" val="OP_ACTIVE"/>
<set name="isDebuff" val="true"/>
<set name="castRange" val="50"/>
<set name="effectRange" val="400"/>
<set name="reuseDelay" val="8000"/>
<set name="hitTime" val="2000"/>
<for>
<effect name="PhysicalMute" time="120" val="0"/>
<effect name="RemoveTarget" noicon="1" val="0"/>
and change to
<skill id="353" levels="1" name="Shield Slam">
<set name="magicLvl" val="77"/>
<set name="weaponsAllowed" val="2"/> <!-- Shield -->
<set name="lvlDepend" val="1"/>
<set name="power" val="25"/> <!-- Base Land Rate -->
<set name="mpConsume" val="35"/>
<set name="target" val="TARGET_ONE"/>
<set name="skillType" val="MUTE"/>
<set name="operateType" val="OP_ACTIVE"/>
<set name="isDebuff" val="true"/>
<set name="castRange" val="40"/>
<set name="effectRange" val="400"/>
<set name="reuseDelay" val="8000"/>
<set name="hitTime" val="2000"/>
<for>
<effect name="PhysicalMute" time="15" val="0"/>
<effect name="RemoveTarget" noicon="1" val="0"/>
Time=in seconds
My Edit
Now shield slam duration is 15 s, was 120s and lower land rate
U can change it as u wish! [better set up and test "how work"]