How do I stop a script after it has started running?

I have made a function that is supposed to play a song and display a message, stop any music that is playing by stopping the sounds in the SoundScape, (which is where I normally put songs) clone then destroy the script that plays the sounds so that it doesn't play any other songs, and afterwards set the cloned script in the work space so that it can run again. This function is supposed to fire when a specific player joins the server and their character finishes loading.

local music = game.Workspace.Music
local creators = {
	"SparkingFruitPunch", "Player2"
}
local already = {}

game.Players.PlayerAdded:connect(function(plr)
	plr.CharacterAdded:connect(function()
		for i,v in pairs(creators) do
		if v == plr.Name and not already[plr.Name] then
			already[plr.Name] = true
			local sounds = game.Soundscape:GetChildren()
			for i = 1, #sounds do
				sounds[i].Playing = false
			end
			local mc = game.Workspace.Music:Clone()
			mc.Parent = game.ServerStorage
			music:Destroy()
			local nega = Instance.new("Sound", game.Workspace)
			nega.SoundId = "rbxassetid://440129799"
			nega.TimePosition = 43.00
			nega.Volume = 1
			nega:Play()
			local m = Instance.new("Message", game.Workspace)
			m.Text = "The creator, "..plr.Name.." has shown himself upon this day!"
			wait(5.30)
			m:Destroy()
			nega:Destroy()
			mc.Parent = game.Workspace
		end
	end
	end)
end)

PLEASE KEEP ALL OF THESE PROBLEMS IN MIND WHEN COMING UP WITH A SOLUTION:

1. I've recently found out that once a script starts running, you can't simply stop it by disabling it, and this script proves that you can't do it by destroying it either (The variable "music" is pointing to a script). How would I stop a script from running?

2. On an actual server, the music does not stop playing. This is strange because inside the function is a for loop that goes through every audio file and makes sure that they're not playing.

3. This is just a hypothesis, but i'm pretty sure if the specified player rejoins the server, this script would error because it has already destroyed the original music script, and the function would ask to destroy it again.

Again, please keep all of these problems in mind when thinking up a solution, because lately people haven't been doing that. (For me at least) Here's the music script if you need it:

local sonic = game.Soundscape.specialStage
local sonicw = sonic.TimeLength
local dbz = game.Soundscape.SoHappy
local dbzw = dbz.TimeLength
local sponge = game.Soundscape.SpongeArcade
local spongew = sponge.TimeLength
local x4 = game.Soundscape.x4
local x4w = x4.TimeLength

while true do
	x4:Play()
	wait(x4w)
	sonic:Play()
	wait(sonicw)
	sonic:Stop()
	wait(5)
	dbz:Play()
	wait(dbzw)
	dbz:Stop()
	wait(5)
	sponge:Play()
	wait(spongew)
	sponge:Stop()
	wait(5)
end

Before I start: Don't fully assume something isn't possible

You obviously don't know some of the few ways to stop a script or even a loop. These include return and break. Aswell as using a Script's Disabled property:

#Using return

Return is neat to use when wanting to simply return a value or maybe even get out of a function. I like to use this often with debounces. Here's more on using a debounce.

--// Say I wanted to make it so the player can only click once ever 5 seconds

local debounce = false --Making a local debounce

mouse.Button1Down:connect(function()
	if debounce == true then --If my debounce is true then
		return --Return out of this function entirely. We stop the rest from running.
	end
	
	debounce = true --Usually goes after the debounce if statement

	--If debounce is false then we can continue with printing...
	print("The mouse was clicked!")

	wait(5) --waiting
	debounce = false -- Setting the debounce so we can enable the player to re-click
end)

#Using break

Like return, break is really simple to use in the same nature of a debounce except they're only used for your while loops, for loops, and your repeat loops. More on using break with loops.

--// You can set this up like a debounce but here's a little copy/paste off wiki on breaks.

while wait() do
   print("hi mom!")
   break -- this forces the endless loop to end
end 

Your script also seems to be missing things that solve your music problem. You seem to be forgetting to stop your music before destroying it in the first script provided.

###Line 26:

wait(5.30)
m:Destroy()

--Adding the :Stop()
nega:Stop()
nega:Destroy()

You can Disable a script that is running at any time by using it's Disabled property. By default, Scripts that are inserted have that property set to false so it's basically always going to start running. If you want to disable it then you can just add YourScript.Disabled = true some where. Setting this back to false after doing this will restart the script.

For your 3rd "Problems to keep in mind". You can easily get out of this situation by cloning the music script and putting it into the player every time they join. Put this in your game.Players.PlayersAdded function. You'll then have the ability to disable it whenever you want.

If you need more elaboration on implementing this into your code then please freely reply on this post.