Is editing anything in /opt/ros/fuerte/stacks acceptable?

edit

I followed this tutorial(The tutorial mentions that it's currently failure, but my question seems irrelevant to the failure), I downloaded the package to my own ros directory.

hg clone https://kforge.ros.org/collvoid/collvoid

However, in the tutorial it mentions patching amcl by

roscd collvoid
mv amcl.patch ../navigation
roscd navigation
patch -p1 < amcl.patch

It moves amcl.patch to navigation package like they are in same directory, for which is in /opt/ros/fuerte/stacks. In my understanding, I should not change anything in /opt/ros/fuerte/stacks, so move amcl.patch to navigation and patch it seems weird to me.

Is there anything wrong with my understanding?

Thanks.