I attempted to create a Valkyrie Lance with additional attack power with this command:

/give @p aether:valkyrie_lance{AttributeModifiers:[{Slot:"mainhand", AttributeName:"generic.attack_damage", Name:"generic.attack_damage", Amount:15.0, Operation:0, }]} 1

The command spawned the lance, but it had none of its descriptors. No base attack, no extended reach, no knockback. It was little more than a stick. I have also done the same with Aether Accessories; namely the Invisibility Cloak, also to no avail.