Provide a way to change the Name of a FormField from the RadDocument.AcroForm.FormFields collection.

As a workaround, you could create a new instance of a FormField with the desired name, add the new field in the document and remove the old one. You can use the following approach:
   1) Create a new instance of FormField (with the desired name, passed in the constructor), which will play the role of a copy of a specific FormField
   2) Copy all properties from the original field (they all vary, depending on the concrete type of the FormField, for example CheckBoxField, etc.)
   3) Create a new widget for the new field, and copy all properties from the original field's widget into the new one.
   4) Remove the original field from the RadDocument.AcroForm.FormFields collection and add the new field.
   5) Remove the original widget from the corresponding page's annotation and add the new one.

Attached is a project demonstrating this approach for a CheckBoxField.