PSCredentialStore/src/Item/Set-CredentialStoreItem.ps1

function Set-CredentialStoreItem {
    <#
    .SYNOPSIS
        Changes the credentials for the given remote host in the store.

    .DESCRIPTION
        Use this function to update your already stored RemoteHost items.

    .PARAMETER Path
        Define the store in which your given host entry already exists.

    .PARAMETER RemoteHost
        Specify the host you for which you would like to change the credentials.

    .PARAMETER Identifier
        Defaults to "". Specify a string, which separates two CredentialStoreItems for the
        same hostname.

    .PARAMETER Shared
        Switch to shared mode with this param. This enforces the command to work with a shared CredentialStore which
        can be decrypted across systems.

    .PARAMETER Credential
        Provided the new credentials you want to update inside the RemoteHost item.

    .INPUTS
        [None]

    .OUTPUTS
        [None]

    .EXAMPLE
        Set-CredentialStoreItem -Path "C:\TMP\mystore.json" -RemoteHost "esx01.myside.local"

    .EXAMPLE
        Set-CredentialStoreItem -Path "C:\TMP\mystore.json" -RemoteHost "esx01.myside.local" -Identifier svc
    #>

    [CmdletBinding(DefaultParameterSetName = 'Private')]
    [Diagnostics.CodeAnalysis.SuppressMessageAttribute(
        'PSUseShouldProcessForStateChangingFunctions',
        '',
        Justification = 'Updates existing credential object.'
    )]
    param (
        [Parameter(Mandatory = $true, ParameterSetName = 'Private')]
        [Parameter(Mandatory = $true, ParameterSetName = 'Shared')]
        [string]$RemoteHost,

        [Parameter(Mandatory = $false, ParameterSetName = 'Private')]
        [Parameter(Mandatory = $false, ParameterSetName = 'Shared')]
        [string]$Identifier,

        [Parameter(Mandatory = $false, ValueFromPipeline = $true)]
        [ValidateNotNullOrEmpty()]
        [PSCredential]$Credential,

        [Parameter(Mandatory = $true, ParameterSetName = 'Shared')]
        [switch]$Shared,

        [Parameter(Mandatory = $false, ParameterSetName = 'Shared')]
        [ValidateNotNullOrEmpty()]
        [string]$Path
    )

    begin {
        # Set the CredentialStore for private, shared or custom mode.
        Write-Debug ("ParameterSetName: {0}" -f $PSCmdlet.ParameterSetName)
        if ($PSCmdlet.ParameterSetName -eq 'Private') {
            $Path = Get-DefaultCredentialStorePath
        }
        elseif ($PSCmdlet.ParameterSetName -eq 'Shared') {
            if (!($PSBoundParameters.ContainsKey('Path'))) {
                $Path = Get-DefaultCredentialStorePath -Shared
            }
        }
    }

    process {
        # Lets do a quick test on the given CredentialStore.
        if (-not(Test-CredentialStore -Shared -Path $Path)) {
            $MessageParams = @{
                Message     = 'Could not add anything into the given CredentailStore.'
                ErrorAction = 'Stop'
            }
            Write-Error @MessageParams
        }

        # Read the file content based on the given ParameterSetName
        $CSContent = Get-CredentialStore -Shared -Path $Path

        $CurrentDate = Get-Date -Format 'u'

        if ($Identifier -ne "") {
            $CredentialName = $RemoteHost = "{0}/{1}" -f $Identifier, $RemoteHost
        }
        else {
            $CredentialName = $RemoteHost
        }

        if (-not($Credential)) {
            $Credential = Get-Credential -Message $CredentialName
        }

        if ($Credential.UserName) {
            if ($null -eq $CSContent.PfxCertificate) {
                $Cert = Get-CSCertificate -Type $CSContent.Type -Thumbprint $CSContent.Thumbprint
            }
            else {
                $Cert = Get-PfxCertificate -FilePath $CSContent.PfxCertificate -ErrorAction Stop
            }

            if (Get-Member -InputObject $CSContent -Name $CredentialName -MemberType Properties) {
                $RSAKey = Get-RandomAESKey
                $CSContent.$CredentialName.User = $Credential.UserName
                $ConvertParams = @{
                    SecureString = $Credential.Password
                    Key          = $RSAKey
                }
                $CSContent.$CredentialName.Password = ConvertFrom-SecureString @ConvertParams
                $CSContent.$CredentialName.LastChange = $CurrentDate
                $CSContent.$CredentialName.EncryptedKey = [Convert]::ToBase64String(
                    $Cert.PublicKey.Key.Encrypt(
                        $RSAKey,
                        [System.Security.Cryptography.RSAEncryptionPadding]::Pkcs1
                    )
                )
                ConvertTo-Json -InputObject $CSContent -Depth 5 | Out-File -FilePath $Path -Encoding utf8
            }
        }
        Else {
            $MessageParams = @{
                Message     = 'Please Provide at least a valid user!'
                ErrorAction = 'Stop'
            }
            Write-Error @MessageParams
        }
    }

    end {

    }
}