I know day-of-travel disruptions (IROPS) are normally resolved by the operating carrier. If hypothetically I face a disruption on a flight purchased from AA.com as AAnnnn operated by AS, must I go to the operating carrier (AS) for rebooking? May I instead go to the ticketing/marketing carrier (AA) -- as I would for issues in advance of travel? Reasons I might prefer this (help from AA on day of travel) include:

• Likely rebooking options would be on AA-operated flights.
• There is an AA lounge with agents to help, but no AS lounge.
• I have status with AA, but not with AS.

Is there a point (T-48?) at which the ticketing/marketing carrier of a codeshare cedes control of the "coupon" (to the operating carrier) and can no longer help with rebooking? Or do they have joint control? Part of my confusion is that I think the ticketing/marketing carrier would be the one to handle a voluntary change/cancellation, even on day of travel.

There is a post about SkyTeam codeshares that says "the ticketing agent is also capable of helping" with IROPS, and a post about Star Alliance awards that says "the ticketing carrier has the absolute right to exchange any of the coupons on the ticket as long as the partner hasn't gone to redeem them".