Well, if you're looking to edit text in the advance games, then use Advance Text, for older games try PokéText, or a hex editor with table support like Thingy32, that works pretty well. With advance games you can add as much text as you want, as the data is repointed to avoid deleting important data, but with a hex editor, don't exceed the existing box of text as it will screw up <_<
Advance text really is a good tool, I would recommend it!