You can edit any phrase in the Recognition Window. Either say "Edit 2" (or the appropriate numbered entry) or click on an entry. Then say "Select The Word <word>" and dictate or spell the corrected word, or double click on the word and type it in. Then say "Choose 2".
Dictate recognizes your speech in phrases, recognizing words in the context of each other. This allows you to speak in phrases, or even full sentences, rather than word-by-word. And when you perform training on an entire phrase, it will gather the context information about all of the words in a phrase, even if you only edit a single word. Even so, I can pass your request for word-by-word training to our product development team. If you'd like to add more detail, please feel free to use the Feature Requests section of these Forums.
btw, Dragon Dictate for Mac (2.0) allows you to say "Train <word(s)>" or "Train That" (for the last utterance), although the Recognition Window behaves the same as v1.5.