An instrument is not editable, but you can change the sound of an instrument extensively by editing a preset. The preset is an incredibly powerful tool that can radically change the nature of an instrument, and the only real limitations will be your imagination! If you get tired of the instruments that are available (which will take a long time since there are over 1000 different instruments in the base sound set) then you can use the Emulator 4 Ultra sampler to create your own, since the Proteus 2000 will soon be able to "read" ROM SIMMs that have been created inside the Emulator 4 Ultra samplers.