expression text

There are different types of expression text, some do indeed go above, but most go below accord to the most widely-followed standard today. Most of the markings above the staff are the ones more specifically called "technical" instruments - things like telling people to use a muta, or play pizzicato. These should be entered as Staff text, not Expressio text. Expression marks that feel related to dynamics go below along with the dynamics. But expression markings that feel related to tempo go above with the tempo. That said, it's a bit subjective.

Anyhow, to flip something between below and above the staff just press "X".