Any way to Edit the Text?

Well, the only surefire method I can think of is to make sure that all of your new dialogue text fits in the same amount of spaces as FF3us's original dialogue.

Alternately, you could ignore the editor and do text-editing the old-fashioned way that the hex-editors of the past did and apply ascii tables to the rom in a hex-editor like WindHex and change it manually, thus making -sure- that you don't overlap any stray map data.