Can a player read a local script thats in another player's character?

I want to know if player A can read a local script inside player B's character and run it from player A's client. If it's not possible, how would you update player B's character on player A's client? (Like when player B's health changes, a billboard GUI shows how much player B's health has changed)

The code that i wrote is like this :

local hum = script.Parent.Parent.Humanoid -- the local script is inside a script
local tweening = game:GetService('TweenService')
local debris = game:GetService('Debris')
local gui = hum.Parent.UpperTorso.GUI
local oldhealth = hum.Health

hum.Changed:connect(function()
    if hum.Health == oldhealth then return end

    local x = math.random()
    local y = math.random()

    if x < 1 and y < 1 then
        if math.random(0,1) == 0 then
         x = 1
        else  
         y = 1
        end
    end

    local tweeninfo = TweenInfo.new(0.5,Enum.EasingStyle.Quint,Enum.EasingDirection.Out,0,false,0)

    if hum.Health < oldhealth then
        local dmgbox = Instance.new('TextBox', gui)
        dmgbox.AnchorPoint = Vector2.new(0.5,0.5)
        dmgbox.Position = UDim2.new(0.5,0,0.5,0)    
        dmgbox.BackgroundTransparency = 1
        dmgbox.BorderSizePixel = 0
        dmgbox.Visible = true
        dmgbox.Size = UDim2.new(0.5,0,0.5,0)
        dmgbox.Font = Enum.Font.Highway
        dmgbox.Text = tostring(hum.Health - oldhealth)
        dmgbox.TextColor3 = Color3.new(255,0,0)
        dmgbox.TextScaled = true

        local tweening = tween:Create(dmgbox,tweeninfo,{Position = UDim2.new(x,0,y,0), Size = UDim2.new(0,0,0,0), TextTransparency = 1})
        debris:AddItem(dmgbox,0.5)
    end

    oldhealth = hum.Health

end)