Adding new functionality to Mbot with out disturbing existing functions

#1

I want to add more programs to Mbot with out disturbing the existing built-in programs set on remote buttons ‘A’,‘B’,‘C’.
For instance, I need to add a new functionality (like playing music) to Mbot when I click ‘D’ button on remote.
I tried uploading a new mBot Program, it worked but I lost all existing functionality of mBot, which should not be the case.
Please provide me guidance for that.

#2

Try this thread:

I don’t think it can be done via Scratch, but you can add capability by editing the source and uploading using the Arduino IDE.

#3