Custom KML Tag

In my rest export field settings for kml format, I'd like to override default field name with a custom - more readable - name. Right now I can chosse a predefined KML tag from the select list. It would be nice to have an new option "Custom" and then a textfield pops up, where you can enter your preferred name.

Example:
Field name: field_bg_blob_yeah
KML Tag: custom
New field name: blobyeah