Of course, as with any large organization, YMMV.
I just came back on an UA-issued award on LH (CDG-FRA). LH doesn't not allow standby and won't change other airline issued ticket. I had an 10 hour connection at CDG. Went to LH check-in asked and nicely to switch to an earlier flight; agent confirmed me on the spot gratis. Shrunk my 10-hour connection down to a 2-hour connection.