Title screen for Doom mods

I'd like to make a Doom mod, but would I have to recompile the game from source to change the title screen? I saw a Doom mod the other day with a title screen, but I don't know how they did it. Is there a program for Doom like FloEdit for Wolfenstein, that will allow one to change the title screen. Or do they have to reassemble the game from scratch to do so?

You can use a program like XWE. You can extract a wad in it. Look for the asset called "titlepic" (or thereabouts). Replace titlepic with your picture and recompile the wad. For making your wad I'd recommend Doom Builder or if your machine can handle it Doom Builder 2.

Thanks for the info, Per-Scan. I got the XWE and managed to create a few Doom mods. Gloomstein has Wolfenstein characters, a character from Heretic, the Pacman character, a couple of characters from Doom2, and Zapper appears as a statue. It is an add-on for Doom. Works best on Doom 1.666. Works okay on Ultimate Doom.
I also updated Pacdoom and Pacdoom2, and added title screens and everything.
All three mods -- Gloomstein, Pacdoom, and Pacdoom2 -- are available at the Acord Games website under "Other Games". http://Acordgames.webstarts.com
Now I'm looking for a good map editor that will allow me to export a map from one wad and import it into another. Any suggestions?
Thanks,
Gary