Add User Name and Password in the Powershell command

You create a mapped drive connection to the remote machine using explicit credentials, edit the file, and remove the connection again.
You can get the credentials using Get-Credential.
Note that you don't need to connect with the logged no user; you just need to connect with any account that has local administrator privileges on the remote machine.

$username = 'JDock'
$credential = Get-Credential -Message 'Logon for the client administrator' -Username $username
$windows7Drive = New-PSDrive -Name Windows7Drive -PSProvider FileSystem -Root "\\windows7\C$" -Credential $credential -ErrorAction Stop
((Get-Content -Path '\\windows7\c$\test.txt' -Raw) -replace ' username', 'white') | Set-Content -Path '\\windows7\C$\test.txt'
$windows7Drive | Remove-PSDrive

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It prompts me to enter Password, I type in the password then I get this error:

PS C:\> C:\changestring.ps1
New-PSDrive : The user name or password is incorrect
At C:\changestring.ps1:3 char:18
+ $windows7Drive = New-PSDrive -Name Windows7Drive -PSProvider FileSystem -Root "\ ...
+ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    + CategoryInfo          : InvalidOperation: (Windows7Drive:PSDriveInfo) [New-PSDrive], Win32Exception
    + FullyQualifiedErrorId : CouldNotMapNetworkDrive,Microsoft.PowerShell.Commands.NewPSDriveCommand

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I got it almost working now. I changed this :

$username = 'JDock'

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to

$username = 'DomainName\JDock'

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However I do not want the prompt to password , can I hardcode it on the script ?

I also am getting :

New-PSDrive : Multiple connections to a server or shared resource by the same user, using more than one user name, are not allowed

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This will store the password securely; it can only be decrypted on the computer where it was encrypted, and by the user who encrypted it.

$username = 'JDock'
## Run the following command on the computer where you want to store the script, and with the user who executes the script.
## It will copy the complete PowerShell command into the clipboard, from where you can paste it and replace the "$password = ..."
## 'Passw0rd' | ConvertTo-SecureString -AsPlaintext -Force | ConvertFrom-SecureString | % {"`$password = '$($_)'"} | clip.exe
$password = '0101...'

$credential = New-Object -TypeName System.Management.Automation.PSCredential -ArgumentList $username, (ConvertTo-SecureString -String $password)

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The "multiple connections" means exactly what it says: you already have a network connection open to the remote machine, but with another user account.
If that happens as well in a freshly opened PS console, you've mapped a drive in Explorer.
You can run a "net use" of connections, and delete them accordingly.
An alternative is the use the remote machine's IP address to connect to (both for the drive and the file read/write).

I used your code above but I am getting this error

ConvertTo-SecureString : Input string was not in a correct format.
At C:\changestring.ps1:13 char:104
+ ... st $username, (ConvertTo-SecureString -String $password)
+                    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    + CategoryInfo          : NotSpecified: (:) [ConvertTo-SecureString], FormatException
    + FullyQualifiedErrorId : System.FormatException,Microsoft.PowerShell.Commands.ConvertToSecureStringCommand
 
New-PSDrive : Multiple connections to a server or shared resource by the same user, using more than one user name, are not allowed. Disconnect all 
previous connections to the server or shared resource and try again
At C:\changestring.ps1:14 char:18
+ $windows7Drive = New-PSDrive -Name Windows7Drive -PSProvider FileSystem -Root "\ ...
+ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    + CategoryInfo          : InvalidOperation: (Windows7Drive:PSDriveInfo) [New-PSDrive], Win32Exception
    + FullyQualifiedErrorId : CouldNotMapNetworkDrive,Microsoft.PowerShell.Commands.NewPSDriveCommand
 

PS C:\> 

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You need to follow the description in the comment. Line 5 needs to be replaced with the contents of the clipboard created in line 4, not with the plain-text password.

Sorry , I am confused. Here is the Script. Please let me know what to change.
Thank you.

$username = 'JDock'
$password='Passw0rd'
ConvertTo-SecureString $password -AsPlainText -Force


$credential = New-Object -TypeName System.Management.Automation.PSCredential -ArgumentList $username, (ConvertTo-SecureString -String $password)
$windows7Drive = New-PSDrive -Name Windows7Drive -PSProvider FileSystem -Root "\\windows7\C$" -Credential $credential -ErrorAction Stop
((Get-Content -Path '\\windows7\c$\test.txt' -Raw) -replace ' username', 'white') | Set-Content -Path '\\windows7\C$\test.txt'
$windows7Drive | Remove-PSDrivecls

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OK, let me ask you a question first: embedding plain text passwords in a script is, as you probably know, not recommended.
You can safely embed a password in PS script, provided it is run on the machine where the password was encrypted, and by the user who encrypted the password.
Now, is that script really safe/temporary enough that you want to embed the password in cleartext, or is that something that will run on a regular basis, and the password should be encrypted?

The Script is one time Run to make changes on the remote computer.

Thank you,

I will test it later