Short answer is "yes". Long answer is yes, but is not trivial. The samples must be compiled into the source code of the firmware. To compile the firmware the user needs to install a proper development tool chain. The sounds must be converted into actual raw data, there are limits on length as well. Some software development skills will be needed to modify the firmware in this way, but we will document the process and possibly build an online tool that converts a .wav file into the appropriate C code to compile into the firmware. Stay tuned.