Assuming the Enterprise Agreement pertains to Volume Licensing, there's no need to perform a clean install if the server is running an Evaluation/Trial edition.
Once the Enterprise Agreement is finalized, you can obtain the keys for Datacenter. However, note that Volume Licensing keys will only work with Volume Licensing media. Ideally, both the keys and ISO should be obtained from the same portal to ensure compatibility.
To avoid reinstalling the operating system for Datacenter and rebuilding the server, you can use a script to convert the Datacenter Evaluation Edition to Retail, then to Volume Licensing. This conversion ensures the Volume Licensing key (Enterprise key) will work as intended.
For more details, visit: Download volume licensing products | Microsoft Learn.