I was planning on writing a detailed tutorial on how to create your own themes, because I just found out myself. I only keep running into
a small problem that I'd like to resolve before I write any how-to.
But the short version is that you need the PocketThemes package (attached below), edit
mytheme.txt in the
example folder (in your case, you will need to change the line
menu.item.5.action=MUSIC, but I don't know the name of the dictionary app; maybe
action=DICTIONARY or some variation might just work) and then run
create.bat to generate the theme file based on your new settings.
You then copy the newly generated
mytheme.pbt (after renaming it to something more recognisable, perhaps) to
/system/themes/ on the PocketBook. After that, you can activate your theme in the PB Settings.
If you find that it works, you can also edit
menu_bg.bmp in the
example/resource/ folder and change the music icon to something that resembles a dictionary. Then generate, copy and activate the theme again.
Good luck!