Cell arrangement cannot be changed without causing exceptions

[HyperLan-git]

First of all, I respect the effort that carykh has made in making this "simulation game" to entertain and let more people learn about biology and virology.

However I am of the philosophy that when you let people get insight on your project and let them access to your source code they should know how to build on that project and make more from it. I have tried to change the cell arrangements in the simulation to test some fun experiments (What if I fill the entire grid with living cells? What if I scale up the map and separate the cells far away from each other?). It is not possible or it's unclear from the provided code how to do that. Of course I've seen this comment in the Cell.pde file :

  /*
  0: empty
  1: empty, inaccessible
  2: normal cell
  3: waste management cell
  4: gene-removing cell
  */

But it doesn't explain clearly what each of these cell types do. 1 is black walls and 2 is living cells but where exactly do I need to put 3 and 4 cells?
I could determine that food particles can only spawn from empty cells (2) and that having none crashes the game. But why can't I manage to have a working simulation where the code for expelling waste doesn't crash the game ? I know cells can't be put on the edges else the waste can get expelled out of the map crashing instantly but theres something else I don't get, probably with those strange seemingly empty 3 and 4 cells.

Thank you again carykh for all your work but I hoped I won't have to spend hours in trial and error and I could get info about how I can modify the simulation without breaking it.
Oh and to modify the cell types I made the function "int getTypeFromXY(int preX, int preY)" in virus.pde return the cell type I want for every tile in the simulation.