onboard memory of usb hid devices "hackable"?

I own some mice and keyboards for example my logitech G400 mouse and my razer deathstalker keyboard.

Both of those devices have as far as i know built in memories to save DPI settings macros so on and so forth.

Now i have read somewhere some time ago that at some german hacker meeting a guy managed to save a keylogger to a razer deathstalker keyboard.

SO my questions are:

1. 
   

   Is the memory built into my razer deathstalker keyboard not secured by a razer digital signature so that it only allows a razer signed driver to save changes to it? Same question goes for my g400 logitech mouse.

   
   


2. 
   

   In case there is none protection whtasoever how could i overwrite the memory by myself? It's a shame that i don't find the original article i read.