OH! I see you already found the forum. Haha. I'll just paste my email here so we can continue the convo here instead.
Okay, that's a tough one but you can definitely do it. I haven't looked at the level editor in probably 5 years now... That would be a good new feature but that editor was just for a "book game", a learning exercise. So, although I feel those two books (VB and C# for Teens) went much further than necessary, and it was crazy fun doing that, some things didn't make the cut. Like, being able to change the tile palette.
You can do it manually inside Visual Basic's form editor. Just replace the Image. Make it exactly like the old one but with new tiles added.
Do you know how to export the tile palette? Okay, your new one should look like that when you insert it into the Image of the PictureBox. In VB, you can literally "paste" the image into there if you have it in the clipboard (via Paint, for instance). Or, use the Image property to load the bitmap file from disk.
And, at this point, my memory is failing on details... I can open up the sources and look at this if it's a huge problem for you. Wouldn't it be cool if you could just add new tiles individually? I based the idea of the editor on MAPPY but wanted more properties just for this particular game (you know like the collision and event names you can type into a tile and so on).
So let me know how it goes and I'll do what I can to help you figure this out. Try first just messing with the Image of the palette. It's just that, a tiled bitmap. You can paste a new one in.