I am sending a custom MIDI string when recalling a preset.
This is OK but every time the iDR recalls any preset, it sends a MIDI command that I do not want.
You need to change the default MIDI channel on the iDR-8In System Manager, go to File, Preferences, MIDI channel number.
Change the iDR-8 MIDI channel number to one that is different to your other equipment.
The custom MIDI command that you have entered contains its own MIDI channel data so will still be on the correct channel.