As in D/P/P or in the HG/SS change information about Pokemon? Which are written in the pokedex. If Bulbasaur, then pokedex wrote: For some time after its birth, it grows by gaining nourishment from the seed on its back. How does it change?
P.S. If that is not so, sorry.
If you want to change the description of a Pokemon, then you need a tool called thenewpoketext. You need to use a getall command to look at all the text to find where the description is. When you find the description file then you need to edit the patch so that the xml looks like this:
And then you can patch your text file.