edit and shadow toolbox function

I need to modify a toolbox file, knowing that if possible it should be avoided. I copied the file to my working directory and issued addpath, checking that the folder is the first in the path list. I issued "rehash toolboxcache". However when I call the function in my script matlab still uses the toolbox function, while I want it to use my modified function: am I missing something?

(I followed the steps described in a similar question)