LF help modifying PQRDealer script Warrior 3.3.5

[IWillSpareNunOfYouPeasants]

Hi,
im using the PQRDealer script for my arms warr on 3.3.5.
The script can be found here:
I tried to modify the pummel script but can't figure out how.
I wanna do the following:
If in battle stance and a two hand weapon is equiped and opponent is casting then switch at 80% of the cast to berserker stance.
Once in berserker stance it automaticly execute the pummel script which is already working.
Since I have no idea how to write scripts I just tried to modify the shieldbash script to cast berserker stance instead:

spell = 2458 --каÑтуемый Ñпелл
target = "target"
Interupts = {   -- Ñпелл лиÑÑ‚ Ð´Ð»Ñ Ð´ÐµÐ¹Ñтвий
---LOCK
6215,  --Fear
17928, --Howl of terror
691,     --Summon felhunter
723,     -- Summon succubus
59172, --Chaos Bolt
47811,   --Immolate
47838, --Incinerate
47843,  --Unstable Affliction
59164,  --Haunt
--SHAMAN
49271, --Chain Lightning
49238, --Lightning Bolt
49273, --Healing Wave
49276, --Lesser Healing Wave
51514, --Hex
--PALADIN
48785, --Flash of light
48782, --Holy Light
--DRUID
48461, --Wrath
33786, --Cyclone
48443, --Regrowth
50464, --Nourish
--PRIEST
48063, --Greater Heal
48135, --Holy Fire
48120, --Binding Heal
48071, --Flash Heal
48123, --Smite
48160, --Vampiric Touch
--MAGE
12826,      -- Polymorph
12824,      -- Polymorph
12825,      -- Polymorph
118,        -- Polymorph
61305,      -- Polymorph: Black Cat
28272,      -- Polymorph: Pig
61721,      -- Polymorph: Rabbit
28271,      -- Polymorph: Turtle
61780,      -- Polymorph: Turkey
42842,                     -- Frostbolt
}
if inMelee(target) and rage>9 and cdRemains(6552) == 0 and NoEquippedItemType("Shields") and GetShapeshiftForm() == 1 or  GetShapeshiftForm() == 2  then
for i=1, #Interupts do
if UnitCastingInfo(target) then
local castName,_,_,_,castStartTime,castEndTime,_,_,castNotInterruptable = UnitCastingInfo(target)
local timeSinceStart = (GetTime() * 1000 - castStartTime) / 1000
local castTime = castEndTime - castStartTime
local currentPercent = timeSinceStart / castTime * 100000
if GetSpellInfo(Interupts) == castName and castNotInterruptable == false then
KickPercent =   80
if currentPercent >= KickPercent then _castSpell(2458,target)
return true
end
end
end
end
end

Unfortunately that script doesn't work.
Does anybody know how to set that up?
i would really appreciate your help.