Usually level 90; if you use a different level when you press 'esc' it will come up with the 'quit to title or Dos' box instead of 'quit y/n'
#Level used for titlescreen, highscores, etc
%patch $9096 $5A $00
And I just found this; this takes advantage of the fact that Keen 1 was supposed to have a demo capability:
#Level 'Restart Demo' switches to
%patch $9086 $5A $00
Normally its the title level, but now you can take a peek into other levels in your mod as well. It will however change the level used for the story, about Id, etc. Also, this stunted code allows:
#Restart demo starts 'presenting and Apogee'... sequence
%patch $9091 $25
And just as an aside:
After game over or game won, high scores are shown in level 16
#But not if acessed from the menu.
%patch $90A8 $01
Enjoy.