I was selecting seats for a friend the other day, can confirm first class cabin is available for selection (no status required).

However - once I'd made the initial seat selection, no further on-line changes were possible. Tried to change the connecting flight and get an error message that it can't be updated.

I had a similar situation with my booking a couple weeks ago - first seat selection held, subsequent changes not possible.

It's possible that at least in some cases, you get one bite at the cherry before having to resort to email.