@harryc123 Here are a couple of ideas:

Review these two Group Policy objects under Administrative Templates > Windows Components > Windows Update

• Remove access to use all Windows Update Features
• No auto-restart for scheduled Automatic Updates installation

The next hack will be to change permissions to a scheduled task. Specifically the one under Task Scheduler Library > Microsoft > Windows >  UpdateOrchistrator | Reboot

1. Go to C:\Windows\System32\Tasks\Microsoft\Windows\UpdateOrchestrator

2. There should be a file named "Reboot" (no extension)

3. Take ownership of it

4. Remove all other user/group from its security properties except you (your login account).

5. Disable the "Reboot" task with administrative powershell Get-ScheduledTask -TaskName Reboot | Disable-ScheduledTask

Also may be useful to have a handy way to collect data about reboot history. Here is a worklet that should help with that:

Function Get-RebootHistory { 
	<#
		.SYNOPSIS
			Retrieves historical information about shutdown/restart events from one or more remote computers.

		.DESCRIPTION
			The Get-RebootHistory function uses Windows Management Instrumentation (WMI) to retrieve information about all shutdown events from a remote computer.  

			Using this function, you can analyze shutdown events across a large number of computers to determine how frequently shutdown/restarts are occurring, whether unexpected shutdowns are occurring and quickly identify the source of the last clean shutdown/restart.

			Data returned includes date/time information for all available boot history events (e.g. restarts, shutdowns, unexpected shutdowns, etc.), date/time information for unexpected reboots and detailed information about the last clean shutdown including date/time, type, initiating user, initiating process and reason. 	

			Because Get-RebootHistory uses WMI to obtain shutdown event history from the system event log, it is fully supported against both legacy and current versions of Windows including legacy versions that do not support filtering of event logs through standard methods. 

		.PARAMETER ComputerName
			Accepts a single computer name or an array of computer names separated by commas (e.g. "prod-web01","prod-web02"). 

			This is an optional parameter, the default value is the local computer ($Env:ComputerName).

		.PARAMETER Credential
			Accepts a standard credential object.

			This is an optional parameter and is only necessary when the running user does not have access to the remote computer(s).

		.EXAMPLE
			.\Get-RebootHistory -ComputerName prod-web01,prod-web02 -Credential (Get-Credential)

			Get boot history for multiple remote computers with alternate credentials. 

		.EXAMPLE
			.\Get-RebootHistory -ComputerName prod-web01,prod-web02 -Credential (Get-Credential) | ? { $_.PercentDirty -ge 30 }

			Get a list of computers experiencing a high percentage of unexpected shutdown events.

		.EXAMPLE 
			.\Get-RebootHistory -ComputerName prod-web01,prod-web02 -Credential (Get-Credential) | ? { $_.RecentShutdowns -ge 3 } 

			Return information about servers that have been experiencing frequent shutdown/reboot events over the last 30 days.

		.OUTPUTS
			System.Management.Automation.PSCustomObject 

			Return object includes the following properties: 

				Computer				
				BootHistory				: Array of System.DateTime objects for all recorded instances of the system booting (clean or otherwise).
				RecentShutdowns			: The number of shutdown/restart events in the last 30 days.
				UnexpectedShutdowns		: Array of System.DateTime objects for all recorded unexpected shutdown events.
				RecentUnexpected		: The number of unexpected shutdown events in the last 30 days.
				PercentDirty			: The percentage of shutdown events that were unexpected (UnexpectedShutdowns/BootHistory).
				LastShutdown			: System.DateTime object of the last clean shutdown event.
				LastShutdownType		: Type of the last clean shutdown event (Restart | Shutdown).
				LastShutdownUser		: The user who initiated the last clean shutdown event.
				LastShutdownProcess		: The process that initiated the last clean shutdown event.
				LastShutdownReason		: If available, the reason code and comments for the last clean shutdown event.

		.NOTES
			Author			: Eric Westfall
			Email			: eawestfall@gmail.com
			Script Version	: 1.1
			Revision Date	: 11/26/2014
	#>

	Param (
						
									)

	Begin {
		$i = 0
		$RecentShutdowns = 0
		$RecentUnexpected = 0

		$BootHistory = @()
		$ShutdownDetail = @()
		$UnexpectedShutdowns = @() 

		# Store original credential, if we attempt to make a local connection we need to 
		# temporarily empty out the credential object.
		$Original_Credential = $Credential

		# Select properties defined to ensure proper display order.
		$BootInformation = @(
			"Computer"
			"BootHistory"
			"RecentShutdowns"
			"UnexpectedShutdowns"
			"RecentUnexpected"
			"PercentDirty"
			"LastShutdown"
			"LastShutdownType"
			"LastShutdownUser"
			"LastShutdownProcess"
			"LastShutdownReason"
		)

		# Arguments to be passed to our WMI call. 
		$Params = @{
			ErrorAction		= 'Stop'
			ComputerName	= $Computer
			Credential		= $Credential
			Class			= 'Win32_NTLogEvent'
			Filter			= "LogFile = 'System' and EventCode = 6009 or EventCode = 6008 or EventCode = 1074"
		}
	}

	Process {
		ForEach ($Computer In $ComputerName) {
			$Params.ComputerName = $Computer

			# You can't use credentials when connecting to the local machine so temporarily empty out the credential object.
			If ($Computer -eq $Env:ComputerName) { 
				$Params.Credential = nSystem.Management.Automation.PSCredential]::Empty
			}

			If ($ComputerName.Count -gt 1) { 
				Write-Progress -Id 1 -Activity "Retrieving boot history." -Status ("Percent Complete: {0:N0}" -f $($i / $($ComputerName.Count)*100)) -PercentComplete (($i / $ComputerName.Count)*100); $i++
			} Else { 
				Write-Progress -Id 1 -Activity "Retrieving boot history." -Status "Retrieving boot history."
			}

			Try { 
				$d = 0
				$Events = Get-WmiObject @Params

				ForEach ($Event In $Events) { 
					Write-Progress -Id 2 -ParentId 1 -Activity "Processing reboot history." -PercentComplete (($d / $Events.Count)*100) -Status "Processing reboot history."; $d++

					# Record the relevant details for the shutdown event.
					Switch ($Event.EventCode) { 
						6009 { $BootHistory += (Get-Date((tWMI]'').ConvertToDateTime($Event.TimeGenerated)) -Format g) }
						6008 { $UnexpectedShutdowns += ('{0} {1}' -f ($Event.InsertionStringsn1], $Event.InsertionStringsn0])) }
						1074 { $ShutdownDetail += $Event }
					}
				}

				# We explicitly ignore exceptions originating from this process since some versions of Windows may store dates in invalid formats (e.g. ?11/?16/?2014) in the event log after an unexpected shutdown causing this calculation to fail.
				Try { 
					$RecentUnexpected = ($UnexpectedShutdowns | ? { ((Get-Date)-(Get-Date $_)).TotalDays -le 30 }).Count
				} Catch { 
					$RecentUnexpected = "Unable to calculate."
				} 

				# Grab details about the last clean shutdown and generate our return object.
				$ShutdownDetail | Select -First 1 | ForEach-Object { 
					New-Object -TypeName PSObject -Property @{
						Computer = $Computer
						BootHistory = $BootHistory 
						RecentUnexpected = $RecentUnexpected
						LastShutdownUser = $_.InsertionStringsn6]
						UnexpectedShutdowns = $UnexpectedShutdowns
						LastShutdownProcess = $_.InsertionStringsn0]
						PercentDirty = '{0:P0}' -f (($UnexpectedShutdowns.Count/$BootHistory.Count))
						LastShutdownType = (Get-Culture).TextInfo.ToTitleCase($_.InsertionStringsn4])
						LastShutdown = (Get-Date((tWMI]'').ConvertToDateTime($_.TimeGenerated)) -Format g)
						RecentShutdowns = ($BootHistory | ? { ((Get-Date)-(Get-Date $_)).TotalDays -le 30 }).Count
						LastShutdownReason = 'Reason Code: {0}, Reason: {1}' -f ($_.InsertionStringsn3], $_.InsertionStringsn2])
					} | Select $BootInformation	
				}			
			} Catch }System.Exception] { 
				# We explicitly ignore exceptions originating from Get-Date since some versions of Windows may store dates in invalid formats in the event log after an unexpected shutdown.
				If ($_.CategoryInfo.Activity -ne 'Get-Date') { 
					Write-Warning ("Unable to retrieve boot history for {0}. `nError Details: {1}" -f ($Computer, $_))
				}
			}

			# Reset credential object since we may have temporarily overwrote it to deal with local connections.
			$Params.Credential = $Original_Credential
		}
	}
}
$rHistory = Get-RebootHistory
Write-Output "Reboot History:"
$rHistory
Write-Output ""
Write-Output "Boot History"
$rHistory.BootHistory
Write-Output ""
Write-Output "Boot Diagnostics:"
$wDiag = Get-Winevent -MaxEvents ($rHistory.BootHistory.count) -FilterHashtable @{
   LogName='Microsoft-Windows-Diagnostics-Performance/Operational'
   ID=100}

foreach ($event in $wDiag)
{
    Write-Output "$($event.TimeCreated) | $($event.Message)" 
}