Changing the Item-Level Permissions Settings for a Document Library requires PowerShell

As it turns out the, setting Item-Level Permissions in a library is fully supported with PowerShell!

The PowerShell commands for changing this are very simple:

$web = Get-SPWeb http://YourSite/
$list = $web.Lists[“Your Document Library Name”]
$list.ReadSecurity = 2
$list.Update()
$web.Dispose()

Note the 3rd line which is where you determine the value for this setting using the following values:

1 = “Read all items”

2 = “Read items that were created by the user”

If you wish to modify the values for Create and Edit access instead, replace .ReadSecurity with .WriteSecurity with the following values:

1 = “Create and edit All items”

2 = “Create items and edit items that were created by the user”

4 = “None”

For example:

$web = Get-SPWeb http://YourSite/
$list = $web.Lists[“Your Document Library Name”]
$list.WriteSecurity = 2
$list.Update()
$web.Dispose()