Convert or remove the delimiter in a MAC Address String.

Convert-MACAddressDelimiter.ps1

function Convert-MACAddressDelimiter
{
    [CmdletBinding()]
    [OutputType([String])]
    Param 
    (
        [Parameter(Position = 0, 
                   Mandatory = $true, 
                   ValueFromPipeline = $true, 
                   ValueFromPipelineByPropertyName = $true)]
        [ValidateScript({$patterns = @(
                                           '^([0-9a-f]{2}:){5}([0-9a-f]{2})$'
                                           '^([0-9a-f]{2}-){5}([0-9a-f]{2})$'
                                           '^([0-9a-f]{4}.){2}([0-9a-f]{4})$'
                                           '^([0-9a-f]{12})$'
                                      )
    
                                      if ($_ -match ($patterns -join '|')){ $true } else { throw "The argument '$_' does not match a valid MAC address format." } })]
        [string]
        $MacAddress,

        [Parameter(ValueFromPipelineByPropertyName=$true)]
        [ValidateSet(':', '-', '.', $null)]
        [string]
        $Delimiter = ':'
    )

    $rawAddress = $MacAddress -replace '\W'

    switch ($Delimiter) 
    {
        { $_ -match ':|-' } { for ($i = 2; $i -le 14; $i += 3) { $result = $rawAddress = $rawAddress.Insert($i, $_) } break }
        '.'                 { for ($i = 4; $i -le 9; $i += 5)  {$result = $rawAddress = $rawAddress.Insert($i, $_) } break }
        default             { $result = $rawAddress }
    }

    return $result
}