how sure we are with this ? at least this is definitely not what the MPO agents said to me every time I booked a companion ticket. they always make sure I understand it very well that I'm sure I want a companion award (double/triple asked a few times), because they said these have different availabilities as normal full award and even if I get confirmed on a companion award, if in the end I want a full award instead, I need to check availability for full award at that point. but, that said, I haven't tried this though, changing from companion to full award in the end...

and, from my experience, it doesn't sound like my companion gets diamond priority, at least not automatically.