I've edited the extensions.cfg and made a few other modifications to my 302. Almost all of the modifications discussed for other models work on the 302.
I've installed fbreader180, which is what led me to modify the extensions.cfg in the first place. With the 15.2 firmware and latest fbreader180, an already good reader becomes very good. I've also installed the hacked Adobeviewer. Make sure you get the one for the 15.2 firmware if that's what you have. Instead of just installing the Adobeviewer as discussed, I renamed it and use the old Adobeviewer for my PDFs. You have to edit the extensions.cfg to get the new one to work with epubs if you keep the old one too. For some reason when I used the hacked Adobeviewer to read PDFs it would always open the previously read book, not the one I selected. So I use the original viewer for PDFs and the hacked viewer for epub. Perhaps it has to do with the fact the one for download came from a PB 360 image. I might try to do the same hack with the viewer on my 302.
One thing about themes. The theme creator was designed for the 301 and it seems that the themes don't work quite as well on the 302. I've been seeing some significant, unexpected changes in the operation of the reader. For example, the context menu when you are reading a book (in most themes) is between 1/3 and 1/2 the size it is in the default theme. And I don't recall any of the other themes having the notes menu choice (the center choice in the grid) available. Half the time the rotate menus are blank in other themes. Even though I like several of the other themes, I've gone back to default just to have full functionality restored. Some of the features in the themes are not needed as much because of the 15.2 firmware. An example is the longer list of most recently read. Clicking the power button brings up a menu that includes the last 10 most recently read books. So I don't need it in my theme.