SchemaMapper Vs AttributeRenamer - Best Practices

For your purpose an AttributeRenamer would be the way to work I think. The SchemaMapper is very complicated, but has usecases other than yours. But I have to admit I ones tried the SchemaMapper but don't remember if I got it to work like I wanted.

Disclaimer, this is only based on my opinion and experience:

I think with more recent releases of FME attribute handling has been improved in a way that has made the SchemaMapper less helpful. Now it's easy to import new attributes easily (as you have found with the AttributeRenamer)

The SchemaMapper is now really only helpful for dynamic workflows in a situation where the file referenced in the SchemaMapper might change. This require more of a dynamic workspace design. I find that I very rarely need to use the SchemaMapper myself.

Hello,

The end goal of our process is to have an automated schema mapping process between the origin schema (which will change) and the destination schema (which will be static). Because the AttributeRenamer is a manual operation to load the fields from file, this transformer doesn't allow us to automate the process.

Hello,

The end goal of our process is to have an automated schema mapping process between the origin schema (which will change) and the destination schema (which will be static). Because the AttributeRenamer is a manual operation to load the fields from file, this transformer doesn't allow us to automate the process.

According to your example you need the BulkAttributeRenamer set to Add String Prefix, Rename, NENA_

Then a NullAttributeMapper with selected Attributes NENA_Field1 NENA_Field2 and If Attribute is empty Map to Missing.

And maybe a BulkAttributeRemover to remove all attributes that don't start with NENA_Field.