As for this ...
[is there a simple way to reset the machine password before taking it off the domain]
The machine password is not the user password. The machine password is provided by ADDS on joining the domain.
The default OS admin account is normally disabled on new systems since Win8 RTM. If you look a the account via Computer Management you see that. So, to even use it you'd need to enabled it first anyway. You really don't need to know that at all, since it is only used once, during new system builds. Just create a new user account. set the password and add it to the LocalAdmin group.
You can use several options to reset any user password on a computer.
Without PowerShell
1. Via computer management
a. Windows Key + X, select computer management, Local Users and Groups, Users, Right-click a user and select set password.
b. Open Windows Explorer, right-click, this PC, select manage, repeat the above.
c. Windows Key + R and type compmgmt.msc and repeat the above
2. via cmd.exe
a. @LPChip already covered regarding 'net user'
b. Using VBScript
2. via PowerShell
a. @LPChip already covered regarding 'net user'
b. The Local User and Group Management cmdlets, you can download from the Microsoft PowerShellGallery.com.
Find-Module -Name '*LocalUser*' | Format-Table -AutoSize
# Results
<#
Version Name Repository Description
------- ---- ---------- -----------
3.0 LocalUserManagement PSGallery a module that performs various local user management function
#>
Find-Module -Name '*LocalUser*' |
Save-Module -Path "$env:USERPROFILE\Documents\WindowsPowerShell\Modules"
Install-Module -Name LocalUserManagement
# Get specifics for a module, cmdlet, or function
(Get-Command -Name Set-LocalUser).Parameters
(Get-Command -Name Set-LocalUser).Parameters.Keys
Get-help -Name Set-LocalUser -Examples
# Results
<#
Set-LocalUser -Name "Admin07" -Description "Description of this account."
$Password = Read-Host -AsSecureString
$UserAccount = Get-LocalUser -Name "User02"
$UserAccount | Set-LocalUser -Password $Password
#>
Get-help -Name Set-LocalUser -Full
Get-help -Name Set-LocalUser -Online
Set-LocalUser Administrator -Password (Read-Host -AsSecureString)
should work in powershell.