LifeMiles Award on UA when having UA Status

I'm considering booking a UA international Economy flight with LifeMiles. I also have UA Platinum status. Would I get free access to Economy Plus right after the ticket is issued (i.e. not only at check-in) even though I booked with LifeMiles? I'd be fine with calling UA to get the seat assignment if necessary.

Does anyone have any actual experience with getting UA status benefits on LifeMiles awards when flying UA?