Powershell to find and rename duplicate values in list items

Is there a way using powershell to find duplicate values in a SharePoint list and rename them as "_1", "_2", "_3", etc.

As an example in my test "Products" list I have the following items:

So for the highlighted items above which have duplicated "SAPMaterial" values, is there a way to use powershell to go through the list to find items that have duplicated values and then if duplicate values are found to then update their "SAPMaterial" value to be like:

• 000000000000227142_1
• 000000000000227142_2

and so on....

The reason I want to find out how to do this with powershell is because we have a list with about 300 items and for quite a lot of these items the values in the "SAPMaterial" column have duplicates. This will take forever doing it manually.

I currently have the following powershell which deletes the duplicates, now we don't want to delete them only renaming them as described above.

#Add-PSSnapin microsoft.sharepoint.powershell
$web = Get-SPWeb -Identity "siteURL"
$list = $web.Lists["Products"]

$AllDuplicates = $list.Items.GetDataTable() | Group-Object SAPMaterial | where {$_.count -gt 1}
$count = 1
$max = $AllDuplicates.Count
foreach($duplicate in $AllDuplicates)
{
$duplicate.group | Select-Object -Skip 1 | % {$list.GetItemById($_.ID).Delete()}
Write-Progress -PercentComplete ($count / $max * 100) -Activity "$count duplicates removed" -Status "In Progress"
$count++
}

Thanks for any suggestions...