Hi aolish,
no, it is not legal to reinstall Windows Server just to reset the 180-day evaluation period.
According to Microsoft's terms and conditions, the evaluation version of Windows Server is intended for testing and evaluation purposes only, and not for use in production environments or for personal use. Once the evaluation period has ended, you must either purchase a license or stop using the software.
Reinstalling the evaluation version to reset the evaluation period is a violation of the terms and conditions and could result in legal consequences. Instead, you may consider using a free trial of Windows Server or purchasing a license to continue your studies.
For more information about how to convert an evaluation version to a retail version, please see Upgrade and conversion options for Windows Server | Microsoft Learn.
Kind regards,
Lei