Substituting other characters

I'm about to start tri-boxing (then move up to 5 boxing when I get everything down) I have a question about substituting in alts into the rotation.

On my main account I have a few alts. For the new setup I'm planning on starting up 3 shaman. My question: Is there a simple solution to substituting in my mage or hunter for a dungeon run. (ie. normal setup 3 shaman, occasional setup 2 shaman and 1 mage) For gear farming.
Macros would be all screwed up. Would it be easier to just have the mage follow one of the shaman? and not participate? Is there a simple solution?
Just wondering if anyone else has tried this.
Thanks

If you use 'focus' targeting, you can just have a different /focus "name" macro to handle swapping out a player. I've been lazy in re-doing my macros, so I'm still using follow/target Party1, and the party leader is my main.

I did some playing around with the setup last night and I think I figured a way to "sub" in another character for runs. (Oh and it was easier than I thought, I fell in love when the first lightning bolt was cast) Multiboxing rocks!

Assuming there's a free action bar (1-0 keys) on the "sub" and add the ranged attack. ie. number '2' is lightning bolt by default, on my mage I would put fireball in the '2' spot
So the mage would atleast be able to contribute to the battle rather than just /follow (2 shaman, 1 mage)

(did I just answer my own question? I am dumb)

in the past what I have done is taken a copy of all the config settings from the toon that is normally integrated with my group, and copy those settings over to the toon that I want to sub in (talking about actually copying files from account\toonA to account\toonB outside of WoW, then starting up the game).

This allows me to have at least roughly the same layout/general macros/keybinds etc already setup. At that point i just start modifying the macros for the new sub toon to match their spells (as you indicated, sync up nukes etc) and then i just remove non-applicable macros (heals on a mage bar get removed so the slots just blank for instance).

I currently just use party1 for all my macros (will be switching to focus with a party1 fallthrough once i get to 70) and I put similar spells on the same place on the hotbar. WIth my locks, they have a castsequence dps "i win" button that I just mash, which coincides with my paladin healer's Flash of Light (targeting the tank's target's target) so I'm always healing the one with aggro (saved my butt a few times) and I just mouse over if I Need to do anything more complex. My mixed class team I went with more of a "casting time" theme, so I have a "long cast" dps button that I use as an opener, and a "short cast" that i spam more often. I also made an "aoe" button which spams consecrate, arcane explosion, fire nova totem, and holy nova. I also just put in a castsequence for my druid to cast instant HoTs sequentally and it's tied to the aoe button, so when im just rolling places and don't want to micro, I just spam that button. I also did some round robin CC macros, which come in handy (given the limitations on certain classes CC,

i find that shamans are really easy to use as the "slaves" so if your subbing in a different class, then make that your main, and simply use keypad for slaves and click on your off class, 20x faster than setting up weird macros for the same numbers, that can easily get you in trouble in a lot of situations. so id say keep a different way of controlling each class ie: shift + anything besides movement keys. ( i use shift + 1-9 for totems :> )