Your asumptions are correct for plane flying with manual throttles (set at constant position, too) and autopilot engaged in AoA hold mode (nonexistant
AFAIK).
In everyday operation planes are flown with autothrottles engaged and autopilot in alt hold mode, so moving from cold to warm airmass will produce slight pitch-up to increase AoA and compensate for lost lift and slight throttle-up to compensate for bit of extra drag and bit of thrust loss. However, those effects are far from signifficant.