I bought a ticket with AY which contains transcontinental economy segments with AA in the US, one with an AA flight number and another as an AY codeshare. I was successful in changing the segment with an AA number to Main Cabin Extra seating (for no charge as an Emerald) by contacting AA directly, but this seems to be impossible for the codeshare segment, as neither AY nor AA can see the seat map for this booking. Has anyone had any luck in getting seat preassignments done (whether in regular Y or MCE), or should I just start expecting to find myself in a middle seat next to the toilet in the last row on the codeshare segment?