Modifying HKCU registry settings at scale presents unique challenges since these settings are user-specific and stored in individual NTUSER.DAT files. The traditional approaches like Group Policy Preferences (GPP) or logon scripts only affect users when they log in, leaving existing profiles and the default profile untouched.

For comprehensive deployment across all existing profiles and the default profile within a specific OU, we need a multi-pronged approach:

1. Targeting Existing User Profiles

# PowerShell script to modify existing user profiles
$users = Get-WmiObject -Class Win32_UserProfile | Where-Object { $_.Loaded -eq $false }
$regKeyPath = "HKCU\Software\YourApp"
$regValueName = "SettingName"
$regValueData = "1"

foreach ($user in $users) {
    try {
        $sid = New-Object System.Security.Principal.SecurityIdentifier($user.SID)
        $userHivePath = "Registry::HKEY_USERS\" + $sid.Value
        
        # Load the hive temporarily
        reg load HKU\TempHive $user.LocalPath
        
        # Modify registry
        Set-ItemProperty -Path "$userHivePath\Software\YourApp" -Name $regValueName -Value $regValueData -ErrorAction Stop
        
        # Unload the hive
        reg unload HKU\TempHive
    }
    catch {
        Write-Warning "Failed to process user $($user.LocalPath): $_"
    }
}

2. Modifying the Default Profile

# PowerShell script for default profile modification
$defaultProfilePath = "$env:SystemDrive\Users\Default\NTUSER.DAT"

if (Test-Path $defaultProfilePath) {
    try {
        reg load HKU\DefaultTemp $defaultProfilePath
        
        New-Item -Path "Registry::HKEY_USERS\DefaultTemp\Software\YourApp" -Force | Out-Null
        Set-ItemProperty -Path "Registry::HKEY_USERS\DefaultTemp\Software\YourApp" -Name $regValueName -Value $regValueData
        
        reg unload HKU\DefaultTemp
    }
    catch {
        Write-Warning "Failed to modify default profile: $_"
    }
}

For enterprise deployment, consider these optimizations:

• Use PSRemoting to execute the script on multiple machines simultaneously
• Implement error handling and logging for each operation
• Schedule execution during maintenance windows as hive loading can be resource-intensive
• Test thoroughly with a subset of machines before full deployment

For environments where PowerShell deployment isn't feasible, consider:

:: Batch file for Group Policy logon script
@echo off
reg add "HKCU\Software\YourApp" /v SettingName /t REG_DWORD /d 1 /f

Note that this only affects users when they log in and doesn't modify existing profiles or the default profile.

When managing enterprise environments, we often need to apply HKCU registry settings across both existing profiles and default profiles for new users. The traditional approach of manually loading each NTUSER.DAT hive becomes impractical at scale.

Here's a robust PowerShell script that handles registry modifications for all existing user profiles:

# Load required assembly
Add-Type -AssemblyName Microsoft.Win32.Registry

# Define registry path and values
$regPath = "Software\YourCompany\YourApp"
$regValues = @{
    "Setting1" = "Value1"
    "Setting2" = 2
    "Setting3" = $true
}

# Get all user profiles
$profiles = Get-ChildItem "C:\Users" -Directory | Where-Object { $_.Name -ne "Public" }

foreach ($profile in $profiles) {
    $ntuserPath = Join-Path $profile.FullName "NTUSER.DAT"
    if (Test-Path $ntuserPath) {
        try {
            # Load the hive
            reg load "HKU\TempHive" $ntuserPath
            
            # Apply registry changes
            foreach ($key in $regValues.Keys) {
                $fullPath = "HKU:\TempHive\$regPath"
                if (-not (Test-Path $fullPath)) {
                    New-Item -Path $fullPath -Force | Out-Null
                }
                Set-ItemProperty -Path $fullPath -Name $key -Value $regValues[$key]
            }
            
            # Unload the hive
            [gc]::Collect()
            reg unload "HKU\TempHive"
        }
        catch {
            Write-Warning "Failed to process profile $($profile.Name): $_"
        }
    }
}

For new users, we need to modify the default profile. This requires booting into the Default User hive:

$defaultProfilePath = "C:\Users\Default\NTUSER.DAT"
if (Test-Path $defaultProfilePath) {
    try {
        reg load "HKU\DefaultTemp" $defaultProfilePath
        
        # Same registry modification logic as above
        foreach ($key in $regValues.Keys) {
            $fullPath = "HKU:\DefaultTemp\$regPath"
            if (-not (Test-Path $fullPath)) {
                New-Item -Path $fullPath -Force | Out-Null
            }
            Set-ItemProperty -Path $fullPath -Name $key -Value $regValues[$key]
        }
        
        reg unload "HKU\DefaultTemp"
    }
    catch {
        Write-Warning "Failed to modify default profile: $_"
    }
}

For environments where PowerShell isn't feasible, Group Policy Preferences (GPP) can achieve similar results:

1. Create a new GPO linked to your target OU
2. Navigate to: User Configuration > Preferences > Windows Settings > Registry
3. Add new registry items with action "Update"
4. Configure the HKCU path and values
5. Enable "Apply once and do not reapply" if needed

• Always test in a non-production environment first
• Consider profile size when working with large NTUSER.DAT files
• Implement proper error handling and logging
• For locked profiles, you may need to use SYSTEM context
• Document all registry changes for audit purposes

For large-scale deployments, consider using a scheduled task running in SYSTEM context:

$action = New-ScheduledTaskAction -Execute "PowerShell.exe" -Argument "-File "C:\Scripts\DeployHKCU.ps1""
$trigger = New-ScheduledTaskTrigger -AtStartup
$settings = New-ScheduledTaskSettingsSet -RunOnlyIfNetworkAvailable -StartWhenAvailable
Register-ScheduledTask -TaskName "Deploy HKCU Settings" -Action $action -Trigger $trigger -Settings $settings -RunLevel Highest -Force