Update-AzureRmTag.ps1

function Update-AzureRmTag {
    [CmdletBinding()]
    param (
        [Parameter(ValueFromPipeline, ValueFromPipelineByPropertyName, Position = 0)]
        [string[]] $ResourceId,

        [Parameter()]
        [hashtable] $Tags = [hashtable]::new()
    )

    BEGIN {}

    PROCESS {
        foreach ($resource in $ResourceId) {
            try {
                $thisResource = Get-AzureRmResource -ResourceId $resource
                Write-Verbose "Processing $($thisResource.Name)"
                if ([bool]($thisResource.Tags.GetEnumerator().Where({$_.Name -notlike '*hidden-link*'}))) {
                    if ($thisResource.Tags.Count -ne 0) {
                        [hashtable]$currentTags = $thisResource.Tags
                        [hashtable]$newTags = $thisResource.Tags + $Tags
                    }
                    else {
                        [hashtable]$newTags = $Tags
                    }
                    $result = Set-AzureRmResource -ResourceId $thisResource.ResourceId -Tag $newTags -ErrorAction Stop -Force
                }
                else {
                    Write-Verbose 'hidden-link found - skipping'
                }           
            }
            catch {
                Write-Warning "[$($thisResource.Name)] $($_.Exception.Message)"
            }
        }
    }
}