Here’s one way to do that: We could give the rule a name and tell Inform that it doesn’t do anything on the first turn, which is when play begins. This construction could come in handy if we want to define additional exceptions later.
Of course, this will also suppress the “Kek” from our Test Scene on the first turn. So if we do want the one “Kek” to show up, we can insert it manually one time when play begins.
Test Scene is a scene.
Test Scene begins when play begins.
When a scene begins (this is the scene-beginning rule):
say “Kek!”.
The scene-beginning rule does nothing when the turn count is one.
The Test Room is a room.
When play begins:
say "Kek (manually inserted)!".
Alternatively, if you don’t need the named rule for other exceptions, you could just say:
When a scene begins:
if the turn count is not one:
say “Kek!”.
(Edited to add: of course, you can also express additional exceptions within that if structure.)