How can my Rage Spirits cast a lower rank spell
 

Sometimes I am only 1-2 Rage short of a spell that would turn the tide of battle completely. Even the lower rank of Evil Shoal can make a difference early on, but whatever...

My question is, how can I make my RAGE SPIRIT cast a lower rank of the spell if I do not have enough rage/power for the max rank?

Sorry, but you can`t. Unlike spells, once it is upgraded, you can only cast the upgraded version.