The AI uses the last choice you choose for WoS. It’s the same for other 2 choices spells IIRC. Oh, troops are different.
You can use it to your advantage: cast WoS in an Explore battle and choose the 2nd spell for curse, then go into PvP with a different weapon, like EoE. The AI will be stuck with WoS’ 2nd spell.
(Still not ideal because now it could be cursing your Elementalist hero and Impervious troops)