Hummm... ok, understood. Just for explain what I tested:
The main ideia is to change the data manipulated by the handler before the handler execute. So I do not have to load all the XML in memory (with the DOM).
But I still have to do a thing! Take all the out that I created(the xml with the changes) and substitute the current XML. For me sounds a little weird and dangerous. But I guess that is the best sollution.
Next, the snippet of the code:
A snippet of the first ContentHandler that 'intercept' the other (called parent). The code, bellow, add a tag 'NEW_TAG' before any element start.