Minecraft – Teleport to spawn in Minecraft creative mode

You could try using the /gamemode <name> 1 command to set your users to be in creative mode. You'll need to do it for each user. Or you could do it like so: /gamemode @a 1 if you want all players to be in Creative mode.

No, this is not possible in an un-modded, single-player game. There's certainly nothing you can do to a map file to force constraints on the player playing it.

Given that people have been playing adventure maps for ages without the special mode, trust has worked very effectively up to this point :-)