Dave Lers wrote:
...I have no idea of the specifics, but there are some email clients where that option is/can be automatically enabled when message text is highlighted prior to hitting reply, e.g. Thunderbird, Claws, OSX/iOS Mail.
Add KMail to that list. I tested Thunderbird, Claws and KMail; all default to quoting highlighted text. Claws defaults to a bottom cursor, KMail and Thunderbird to a top. All can be reconfigured.