Hi Dean,

In UI for Blazor 2.30. we released a couple of export events that allow you to customize the exported file:

• OnBeforeExport - you can handle that to make specific file customizations based on the built-in options. For example, set the width/format of the columns, specify which data to be exported.
  
  
• OnAfterExport - this event provides access to the output of the exported file as a memory stream. This gives you full control to perform any desired customizations using the RadSpreadProcessing library, for example.

I hope you will find the above information useful. Take your time to revise and test the customization options and please let us know if any other questions appear.

In the meantime, we will consider documentation improvement, so these details are more easily discoverable. 

Regards,
Nadezhda Tacheva
Progress Telerik

A workaround option could be creating the file with your own code, you can see an example of doing that in my post from 13 Jan 2020  here.

Regards,
Marin Bratanov
Progress Telerik