If an 1 bar part are created on a miditrack, and an program change are created in the routing section, if copying that part, changing program change in one or the second part, will change program change in the other part.
Do you mean in the same track? If you set the Progeam Change in the Inspector, it sends the MIDI Message until you send another Program Change as common MIDI Data (within the MIDI Part).
Same track, but different parts.
Does the other MIDI Part include the Program Change MIDI Message?
That usually happens when the parts are “shared copies”.
Which version of Cubase do you use?