Wouldn't it be easier just to have 5 separate keys for target specific chars.

have one key
with the macro
Code:
/target some char name
/target some other char name
...
have all chars names of one account there
do this for all 5 accounts

then setup another set of keys for greater heal shield ...

that way it takes 2 key press to do any combo
then when yeh add another char all yeh gotta do is add em into the /target macro