If you a referring to the examples there is no difference, both the TextExample and ChangeableTextExample both derive from the Class Text.
All the ChangeableTextExample is showing is how to change the contents contained with your string.
Question
What is the difference between Text and ChangeableText in andengine. Since there is no andengine manual i couldnt find the information anywhere
Solution
If you a referring to the examples there is no difference, both the TextExample and ChangeableTextExample both derive from the Class Text.
All the ChangeableTextExample is showing is how to change the contents contained with your string.