Question about match-up conditions

[Naito-desu]

Admittedly, I have not read the rules extensively but I'm thinking about things like setting it in an arena like a sky island where characters have no conceivable way of getting back into the fight when knocked off without flight, or making it a tournament context where knock-out is valid but killing counts as a loss.

How flexible can a match-up be before it cannot be added? Just curious