I am unable to find any rules that govern the manipulation of tetras on the ground.
Certainly, the vision tetras must be manipulated, as they begin on the ground. Furthermore, since it is possible to descore tetras within the goals, it follows that it should be possible.
But are there any other restrictions? Can they be used as blocking mechanisms? Et cetera.
–Petey
I believe so. We had at least three people on laptops with the rules, ensuring any strategy ideas we had were legal, and that was one of the things we thought of… 
I’m interested that they weren’t more explicit. If memory serves, they were far more restrictive with the Stack Attack challenge, which was quite similar.
Ah well. More stuff to do, then.
–Petey
I havnt found anything aside of damage to the field that would limit you in the manual.
You can pull any tetras that are lying on the floor, inside of a goal out. That’s the only descoring of tetras you can do.