“Amazoness Spellcaster” targets (it targets 2 monsters), so when you activate “Amazoness Spellcaster” you select 1 face-up Amazoness on your side of the field and 1 face-up monster on your opponent’s side of the field.
You can select “Gradius’ Option” as the other monster, and the original ATK of the Amazoness will now be the ATK of “Gradius’ Option” at the time “Amazoness Spellcaster” resolves. The ATK of “Gradius’ Option” remains as the ATK of “Gradius” and does not become the ATK of the Amazoness.
If you activate “Amazoness Spellcaster”, and chain “Dramatic Rescue”, “Amazoness Spellcaster”’s effect disappears.
If you switch ATKs with “Amazoness Spellcaster”, and one of the monsters is equipped with “Megamorph”, after the switch, you change the ATK of the monster that is equipped with “Megamorph” using the effect of “Megamorph”.
With “Shield & Sword”, since these are both Normal Spell Cards, you resolve them in the order of their activation, and recalculate their ATKs in that order.