You need a couple things. One of the following: SCI Decoder VGA, SCI Studio VGA, or SCI Resource Viewer to extract the proper Graham sprites. Then you need either SCI Graphic Studio, SCI Studio VGA, or SCI View256 Editor to actually edit them. The TEXT resources you can just extract and edit with SCI Studio, I believe. I don't think the format has changed at all between SCI versions, I could be wrong. Either way, you can edit the TEXT resources with a text editor no problem. Course, you have to know which lines are Graham's. Shouldn't be too hard to figure out.
I've managed to extract them and open them with SCI graphic studio, but after I edit them, how do I put them back in the game? I know it seems silly, but I've never done this sort of thing before.
EDIT: Nevermind, I figured it out.
Till next time stay cool