Was the deadline moved or is the countdown bugging?
Texture and lighting changes are fine. The main structure needs to remain, although it can be modified. You can use your own judgement about whether it's in the spirit of the competition. I can't guarantee that making it completely different from the base map won't count against you in judging, it's all subjective. Put it in space, sure, but make it an asteroid or something so the canyon can remain.