custom voice implies a sound already in sound memory? If that is the case either the entire sound memory can be saved and added to other composer/panel memory etc setups, or a single sound memory written into another sound memory in another setup file.

To save the entire sound memory, Save, Technics, Page 2, press All Off, press Sound YES, name file and press Save. Now this sound memory can be loaded on top of an existing setup just replacing the sound memory, but not affecting composer, panel memory, anything else etc.

To load a single sound memory into a new file or existing setup FIRST load the existing setup. Now go to the new file with the new sound (which must be in 7k format), Load, go to Page 3, press Mode until Sound Memory appears at the top, confirm the right lower button says Single, on the left From select the memory number of the new edited sound, on the right To select the sound memory number you want the sound to appear, press Load. The new single sound memory is now in the existing setup without affecting the other 39 sound memories or composer/panel etc etc, just save the setup normally with the new sound.