Welcome to Librarium Online!
So my question revolves around have a unit that is frenzied with a frenzied hero.
For example, 10 Warriors of Chaos with MoK with an Exalted hero with MoK.
In range of this unit are two enemy units. So by rules of frenzy I would get to pick which I declare my compulsory charge against.
Can I declare my hero as charging one of the two units, and the warriors charging the other?
nope pg 78 "he has no choice but to accompany them when they charge" or pg73 "if a character is with a unit when it declares a charge he must charge with it"
Just a note of warning, frenzied characters can be a god awful idea.
Consider the scenario of a unit of Wood Elves, White Lions, or any skirmishing unit in a wooded area in sight of a unit of frenzied warriors, say 5-6" away, and say also that the warriors will have to make a slight wheel to charge.
So you declare your charges, and then check for frenzied charge range. You both decide that the frenzied warriors don't have to declare a charge since the wheel, combined with the half movement penalty of the woods, means that the skirimishers/wood elves/what-have-you are not in charge range of the frenzied unit.
But Ho! You have a frenzied character, who, if he were to charge out on his own (and therefore would become a skirmisher, ignoring wooded terrain penalites) is easily in charge range of the unit, and charging out he goes. Your enemy, if it's a rnaked up unit, will take that 5 or 6 attack charge and stand a good chance of beating him in combat, or will flee, leaving your character out in the open to be shot or magiced to death.
Frenzied units can be great if you know how to use them (I've found out that I don't), but the only real benefit to a frenzied character is the immune to psychology aspect of it (+1 attack for just a single model is no show stopper,) which he gets automatically by joining an ITP unit.