Here’s another variation …
#1..100 | foreach { "pass$psItem" } >> source.txt
$pass = Get-Content .\source.txt -TotalCount 1
$newList = Get-Content .\source.txt | select -Skip 1
$newList | Out-File .\source.txt
Here’s another variation …
#1..100 | foreach { "pass$psItem" } >> source.txt
$pass = Get-Content .\source.txt -TotalCount 1
$newList = Get-Content .\source.txt | select -Skip 1
$newList | Out-File .\source.txt