For extras - absolutely go ahead and do whatever else you'd like for them.

For main assignments - I'm a little worried that recipients might feel like whatever they receive wasn't really created for them if it starts showing up in other challenges, so I'd kind of prefer if they could be kept just for space_swap. If it's just a matter of linking something for points, I think that's okay, but otherwise I'd rather not see these things re-used. Does that make sense?

Of course, you can repost your work wherever you like once everything's revealed!