I have never seen mention of such a command, and I'm not sure there is any point as it's such a trivial task to send midi data to set the channels of ANY device to whatever.
Some devices do set channels to specific instruments on startup or reset, but this is probably different for each device. This may be detailed in the respective manual.
The current setting, where this is stored, would be at a specific memory location in the RAM of the device, but this location will be different for each device. A SysEx command could probably be created to read (and return) this data as a SysEx data dump, but it would need to be different for each device.
As I suggested, the simplest solution would be to create a small midi file that does nothing but send the PC commands to set each channel to your preferred defaults, and 'play' that file before doing anything else. Then you KNOW what the settings are.