How would I change the characters in a value, like if i have _c8_ change the _ to a letter?

Namee = script.Parent.Namee

Nameo = script.Parent.Nameo

--Characters Here:

local characters = {"_", "q", "w", "e", "r", "t", "y", "u", "i", "o", "p", "a", "s", "d", "f", "g", "h", "j", "k", "l", "z", "x", "c", "v", "b", "n", "m", "Q", "W", "E", "R", "T", "Y", "U", "I", "O", "P", "A", "S", "D", "F", "G", "H", "J", "K", "L", "Z", "X", "C", "V", "B", "N", "M", "1", "2", "3", "4", "5", "6", "7", "8", "9", "0"}

--Length Here:

local charLength = 1

local cache = {}

--/CONFIGURATION--

local Ui = script.Parent.Parent.ScrollingFrame

--You Will See Random Generated Word In Output Window

--To Start It Disable This Script And Enable

  

while true do wait()

local word = ""

for i = 1, charLength do

local randNum = math.random(1, #characters)

word = word .. characters[math.random(1, #characters)] .. characters[math.random(1, #characters)] .. characters[math.random(1, #characters)] .. characters[math.random(1, #characters)]

print(word)

Nameo.Text = word

wait()

word = ""

end

local Players = game:GetService("Players")

local cache = {}

function GetUserIdFromUsername(name)

-- First, check if the cache contains the name

if cache[name] then return cache[name] end

-- Second, check if the user is already connected to the server

local player = Players:FindFirstChild(name)

if player then

cache[name] = player.UserId

return player.UserId

end

-- If all else fails, send a request

local id

pcall(function ()

id = Players:GetUserIdFromNameAsync(name)

end)

cache[name] = id

return id

end

if (GetUserIdFromUsername(Nameo.Text)) == nil then

Namee.Text = ("Not Taken")

local addtolist = Instance.new("TextLabel")

addtolist.Parent = Ui

addtolist.BackgroundTransparency = 1

addtolist.Size = UDim2.new(5, 0, 5, 0)

addtolist.Text = Nameo.Text

script.Parent.Image = "rbxassetid://891981050"

else

Namee.Text = (GetUserIdFromUsername(Nameo.Text))

script.Parent.Image = "http://www.roblox.com/Thumbs/Avatar.ashx?x=200&y=200&Format=Png&userid="..(GetUserIdFromUsername(Nameo.Text))

end

end

I have tried using strings but it didn't work, and I don't even know if there is a way. Nameo is the value because it comes back like i said in the title, sometimes.

I added this below Nameo.Text = word and above wait()

if Nameo.Text == string.sub(1,1) == "_" then

Nameo.Text = "null"

end

if Nameo.Text string.sub(4,4) == "_" then

Nameo.Text = "null"

end

It didn't work...