Before creation, you will need to modify the standard.
For the option of changing after (or during) creation, you can go to Tools -> Options -> Mechanical Design -> Drafting -> Manipulators, and turn on the features that you want to modify. (I usually turn them all on, but only "after creation", or "modification", to be precise)
With the manipulators turned on, you simply select the dimension, and you can pull, tug, or click for text addition. Very nice feature.
