Use Alt+, as the standard keyboard shortcut to invoke KDE programs' "Configure <Program>" menu items. Right now there is no shortcut defined for this, which is a shame because having a standardized shortcut for it is really useful, and we actually have the opportunity to do so because our software uses KStandardActions for these kinds of things.
As a side effect, this happens to preserve former Mac users' muscle memory, since on that platform the shortcut is Command+, and the Alt key on a PC keyboard is in the same location as the Command key on a Mac one.