Is it possible to set Windows Administrator password via User Data Script?

Hello.

You can change your password using your user data as described below.
However, you will no longer be able to obtain a new password using the Amazon EC2 console as described in the following documentation.
https://docs.aws.amazon.com/AWSEC2/latest/WindowsGuide/ec2-windows-passwords.html

Store the new password in a safe place. You won't be able to retrieve the new password using the Amazon EC2 console. The console can only retrieve the default password. If you attempt to connect to the instance using the default password after changing it, you'll get a "Your credentials did not work" error.

<powershell>

net user Administrator "New Password"

</powershell>