Calling Cast function on player doesn't equip the spell but casts it
In openMW calling the cast function on player doesn't trigger a cast animation but casts the spell on its target if it's on self or on touch, or sends the spell projectile in the cursor direction if it's on target.
Vanilla doesn't trigger that. When using cast on player, a quirk of vanilla is that it lets you equip any spell on the player, even if it's not known, meaning it's ready to be cast until another spell is selected
player->cast "telekinesis" player
I'm not sure if that quirk is used by mods