I want to change only the file extension

[BTskj]

Hello.

I usually use Save to Disk.

This method allows me to choose file type conversion, but there is no way to change and save only the file extension.

I'd like to change only the file extension with one click and save it to disk.
(Specifically, from .kepub to .epub)

Please let me know if you know technique or plugin

Thank you very much for reading to the end