The Sprites Editor (F6)
Once again, like the sounds editor, this provides a useful look up table. In this case, all the sprite sets are listed so if you want to find out the correct sprite number to enter in the frames table to use, say, the POSS series of graphics, you can find out here (or you could check the tables on my page) :-).
The only editable column is the text offset. Again, I have never needed to edit this, but you can hit j to jump to a screen where you can edit the sprite names (just a section of the text editor - F7). On that screen you can change TROO (the imp series of sprites) to your own preferred name. From that point on, when a frame looks for sprite series 0, it will look for your entered name rather than TROO. This screen will allow names of more than 4 letters to be entered. Doom sprites all have a 4 letter start sequence to identify them, so stick to 4 letters.