I would love to be able to control the size of mobs from mods that have variable size ranges (Such as ZAWA, Dr. Zharks, Lycanites, etc). If this is possible with the current format I'm not aware of how to utilize it.

Sadly there is no current way for someone to increase the size of a mob's hitbox or size appearance. The only way to increase any size would be through glitches with commands if you are interested:
video explaining it better

unless you can somehow do it with the nbt action that I don't know about, it is not possible
nbt actions

-note I am not the mod creator