How To Make The "TF2 Sol. Roc. Launch." Model's Blast Pressure Change If Owner of RPG Gets Hit?

I'm not exactly sure how to explain this besides saying that I copied and pasted your lines right before they set the explosion's blast pressure, I can surely explain if you have any specific questions though.

-----------------
--| Constants |--
-----------------

local BLAST_RADIUS = 7
local BLAST_PRESSURE = 0

local IGNORE_LIST = {rocket = 1, handle = 1, effect = 1, water = 1} -- Rocket will fly through things named these
--NOTE: Keys must be lowercase, values must evaluate to true

--------------------
--| WaitForChild |--
--------------------

-- Waits for parent.child to exist, then returns it
local function WaitForChild(parent, childName)
    assert(parent, "ERROR: WaitForChild: parent is nil")
    while not parent:FindFirstChild(childName) do parent.ChildAdded:wait() end
    return parent[childName]
end

-----------------
--| Variables |--
-----------------

local DebrisService = Game:GetService('Debris')

local Rocket = script.Parent

local CreatorTag = WaitForChild(Rocket, 'creator')

local SwooshSound = WaitForChild(Rocket, 'Swoosh')

-----------------
--| Functions |--
-----------------

-- Returns the ancestor that contains a Humanoid, if it exists
local function FindCharacterAncestor(subject)
    if subject and subject ~= Workspace then
        local humanoid = subject:FindFirstChild('Humanoid')
        if humanoid then
            return subject, humanoid
        else
            return FindCharacterAncestor(subject.Parent)
        end
    end
    return nil
end

local function OnExplosionHit(hitPart)
    if hitPart then
        local _, humanoid = FindCharacterAncestor(hitPart.Parent)
        if humanoid and humanoid.Health > 0 and not game.Players:GetPlayerFromCharacter(humanoid.Parent) then -- Checks if the humanoid hit is a player
            CreatorTag:Clone().Parent=humanoid
            humanoid:TakeDamage(100)
        end
    end
end

local function OnTouched(otherPart)
    if Rocket and otherPart then
        -- Fly through anything in the ignore list
        if IGNORE_LIST[string.lower(otherPart.Name)] then
            return
        end

        -- Fly through the creator
        local myPlayer = CreatorTag.Value
        if myPlayer and myPlayer.Character and myPlayer.Character:IsAncestorOf(otherPart) then
            return
        end

        OnExplosionHit(hitPart)

        -- Boom
        local explosion = Instance.new('Explosion')

	if hitPart:IsDescendantOf(CreatorTag.Value.Character) then
   		BLAST_PRESSURE = 100000
	else
   		BLAST_PRESSURE = 0
	end

        explosion.BlastPressure = BLAST_PRESSURE
        explosion.BlastRadius = BLAST_RADIUS
        -- todo configure based on proximity
        explosion.DestroyJointRadiusPercent = 0

        explosion.Position = Rocket.Position
        explosion.Hit:connect(OnExplosionHit)
        explosion.Parent = Workspace

        -- Move this script and the creator tag (so our custom logic can execute), then destroy the rocket
        script.Parent = explosion
        CreatorTag.Parent = script
        Rocket:Destroy()
    end
end

--------------------
--| Script Logic |--
--------------------

SwooshSound:Play()

Rocket.Touched:connect(OnTouched)

-- Manually call OnTouched for parts the rocket might have spawned inside of
--TODO: Remove when Touched correctly fires for parts spawned within other parts
local partClone = Rocket:Clone()
partClone:ClearAllChildren()
partClone.Transparency = 1
--partClone.Anchored = true --NOTE: DOES NOT WORK if part is anchored!
DebrisService:AddItem(partClone, 0.1)
partClone.Parent = Workspace
partClone.Touched:connect(OnTouched)