Secret exit when engine supports an exit to non-standard map number

[NaturalTvventy]

Let's say you want to put in an secret exit to a non-standard map number (e1m0, or map33, say), but only have it accessible to as many engines as possible that support those map slots and exits to non-standard map numbers. Otherwise the map should be compatible with any limit-removing engine. 1) Can it be done? 2) How? I'm thinking objects blocking passages in limit-removing that aren't there in more advanced engines. But is that even possible?

[Gez]

You can use a non-vanilla linedef for the secret exit action. Vanilla safely ignores unknown linedef types (contrarily to unknown sector types). For ZDoom you can define new linedef types with xlat; for Eternity you use ExtraData; for Doomsday you use XG.