You asked if it could "impact" the stock which is commonly understood as meaning a downward impact. Even setting aside the fact that they are different companies, I don't see how a successful demonstration could do that, no. If anything, if you want to make it about Musk and not the specific companies, it should give people more confidence in Musk since it went exactly as planned.
Impact per google: “2. have a strong effect on someone or something” No indication of direction. Lacking this distinction, the direction is implicit from a successful test to be positive.
