Final answer:
The alternative method to undo changes from an unattend file involves manual reversion of settings or a system restore, both of which are time-consuming due to the detailed knowledge required and the data processing involved.
Step-by-step explanation:
The alternative method to undo changes made using an unattend file on a Windows system is to manually reverse the settings or to perform a system restore to a point before the unattend file was applied. The reason this might take more time is that manually changing settings requires detailed knowledge of what was changed and how to revert each setting. Additionally, a system restore can be time-consuming because it may involve significant data processing and potential data reversion for all system changes made since the restoration point, not just the unattend changes.