Are we agreed that, if the cg of the released payload is longitudinally-coincident with that of the aeroplane, then the resultant lift/mass acceleration will be upwards along the normal axis; ie, no change to pitch angle?
A load released aft of the aircraft's cg would cause a pitch down in addition to the upward vector; fwd of the cg a pitch up.
Other things being equal, of course, if the resultant upward acceleration were along the normal axis this would alter the relative airflow vector to effectively reduce alpha on the wing, reducing lift. However, the horizontal stab would undergo an increase in negative alpha, causing the aircraft to pitch up, and at this point my tiny brain is beginning to lose the plot .........