It looks like you are basing all your targetting on group position (party1, party2, etc). Just wanted to throw out another option...

If there are only a small number of potential team swaps like mine is, you can also try something like:

/target TankA
/target TankB
/cast Greater Heal

It will look for TankA first, then TankB, to find whichever one exists. This of course assumes that both won't be in the party at the same time, or at least the tank at the bottom of the stack is the one that would be the primary heal target.

A sample attack macro for my shaman is:

/assist Luan
/assist Arvault
/castsequence .....

When I'm in my full 5-man configuration, all these types of commands default to my tank (Arvault) as the leader. But when I run with my brother as tank and me following in a 2-man or 3-man DPS configuration, then they will all target off of my mage (Luan), since Arvault will not be found. This way I don't need to change any targetting macros, though I do sacrifice some flexibility by doing this as I need to have specific names in the macro. If you're expecting to run with a greater variety of characters, then I wouldn't recommend this approach. Also, I use up more of the macro character limit on targetting, but this hasn't been a problem for my setups and rotations (except my warlock, but he's being replaced by boomkin).