Well, I'm not sure what text editors the n900 comes with that are more user friendly (mine is still on route to me), but if you have a text editor you need to open the file it in that and use it - which I guess has complications added if the file has restricted permissions from the root user.

Try

sudo nano /etc/hildon/..(type the filename here or copy paste it)

If you know what your editor is called, try typing that instead of nano - that's just an example and I'm doing this on an N95...

Please excuse me, I don't guarantee and not even confident that this won't break the file ownership. Careful!