Is it possible to modify the destination of a portal to a random location in a world?

Take a look at #42, maybe that's useful for you.

But if you look at larger areas, you quickly get far above billions of blocks. And if we don't want to teleport players into instant death (high up in the sky or in the ground), we have to check all of those blocks. Manually. And I don't assume that you want to have your server locked up for a few hours everytime somebody uses that teleport destination.