If you just want to remove all KDE games from the menu, just list their .desktop files:
Code:
kdegames=$(grep Game /usr/share/applications/kde4/*|grep Categories|sed "s/:.*//")
Then, use a sed script to insert a line with a NoDisplay=true key in each file, either in place for all users, or in a copy in /home/$(whoami)/.local/share/applications for a specific user.
Alternatively, to show them only in the KDE menu include the key OnlyShowIn=KDE;
Cf. the
Desktop Entry Specification.