It looks like "KDE" and "kde" are both defined several places in kcmdlineargs.cpp for parsing purposes. Furthermore, the following files in tdelibs alone use or provide this string in the command line context: tdelibs/tdecore/kcmdlineargs.cpp tdelibs/tdecore/kuniqueapplication.cpp tdelibs/tdecore/kapplication.cpp
To directly answer your question, the text string itself is defined in kapplication.cpp:1566, but modifying the text string means that the other files I mentioned must also be modified.
Hope this helps!
Updated in GIT hash 554196e4. :)
Darrell