Remove permissions for a security group for all files and folders in a folder and all subfolders?

Question

I found a script that adds rights to files and folders.
We need to grant administrators rights to a set of folders for a specific project.
ChangePermissions.ps1
# CACLS rights are usually
# F = FullControl
# C = Change
# R = Readonly
# W = Write
$StartingDir=
"C:\Users"
$Principal="Administrators"
$Permission="F"
$Verify=Read-Host `n "You are about to change permissions
on all" `
"files starting at"$StartingDir.ToUpper() `n "for security"`
"principal"$Principal.ToUpper() `
"with new right of"$Permission.ToUpper()"."`n `
"Do you want to continue? [Y,N]"
if ($Verify -eq "Y") {
foreach ($file in $(Get-ChildItem $StartingDir -recurse)) {
#display filename and old permissions
write-Host -foregroundcolor Yellow $file.FullName
#uncomment if you want to see old permissions
#CACLS $file.FullName
#ADD new permission with CACLS
CACLS $file.FullName /E /P "${Principal}:${Permission}" >$NULL
#display new permissions
Write-Host -foregroundcolor Green "New Permissions"
CACLS $file.FullName
When the project is over, we need to undo the changes and remove administrators permissions from the same group of folders.
How do we change the script to remove administrators group members instead of adding?

Answer 1

I'm not sure I understand how to use that example script to undo the changes in the script I posted..
Is there  a way to just change a few lines in the first script so that it removes instead of adding the administrators group?
This line appears to be the line that adds permissions:
#ADD new permission with CACLS
CACLS $file.FullName /E /P "${Principal}:${Permission}" >$NULL
What would be the syntax to remove the  permissions
$Principal="Administrators"
$Permission="F"
 from files and folders in $StartingDir= "C:\Users"
and everything below it?