Reverting to default firmware - ATMega 8u2

Hey all,
I am absolute beginner in this field so pardon me if this is a obvious question;
I want change the firmware of the ATMega 8u2 to be use as a mouse, for which i have found a couple of good tutorials.
If i change the firmware can I revert to the original firmware that comes with the Arduino ?
Logically it would seem that I can but I just want to be sure.

Thank you for any reply,

If you figure out how to flash the modified firmware, the original firmware is available for you to flash back, so yes, you can revert.
If the new firmware supports the protocol to update the chip over USB, you might not even need to use the ICSP pins.

Thank you for your reply.
I just needed some reassurance, was afraid to turn my uno into scrap but now shall do it
Thanks again

This topic helped me reflash my firmware on my nearly fried/unrecognized Arduino Uno! Thanks! XD