I don't use the Focus or Numbering... The problem with those approaches is that it doesn't work when you group with others, for example Instant Adventures, PvP Warfronts, Rifts, Zone Events, etc. Depending on how it's done, it can also be difficult to swap leader effortlessly.

I use FTL modifiers instead, which both IS-Boxer and Rift supports. So I actually have 5 assist commands in my assist macro. Something like:

Code:
assist [shift] MyChar1
assist [ctrl] MyChar2
assist [alt] MyChar3
assist [shift] [ctrl] MyChar4
assist [shift] [alt] MyChar5
Then I can seamlessly change to a new main character and everyone will assist him instead. This is because IS-Boxer can automatically add the SHIFT key if I'm on MyChar1, or add the CTRL key if I'm on MyChar2. Rift will only execute the line that matches the currently "pressed" modifier keys.