how to create a new part with new clef without affecting that part in the score and without changing the clef in the original part

I've twice tried to do this:
1. by duplicating the part, then changing the clef.
2. by creating a new blank part and opening up the "eye" to reveal the appropriate part then changing the clef.

But each time, the original part and the score are changed to the new clef.

In summary:
I would like "Alto instrument 2" in the score to remain in alto clef.
I would like to create the following parts with their specified clefs:

Alto instrument 2 (alto clef)
Alto instrument 2 (treble clef)

The score attached now has all these parts in treble clef.