nah, you'd just write multiple functions.
Function-whatever_mabi1-
Winactivate mabi1
do the job
sleeptimer to allow next window to activate
end function.
It'd be pretty effective with a farming bot for instance, as if you're multi clienting (Old school multiclienting I mean), you possibly have a bypass, and thus it doesn't matter how many clients you are running, as the HS cpu clock desync QQmoar will not activate.
Assuming logging into an account and performing a farming action takes 2 minutes, which I find quite feasible, and you timed it perfectly, you could do about 90 accounts per client every day.
27,000,000 gold per client, per week.
You could have a cascade effect on the clients, whilst one action is being completed, the next account is being prepared, etc.
If you could get the control send(It was something like that.. doesn't require the window to be active.) that someone else mentioned working for mabi, you could quite literally have no limitation on how many bots/scripts were currently running, provided you renamed each window.
Edit:
Forgot to mention, if you meant multiple OS user accounts, unfortunately that will not work, HS can recognise that it's running elsewhere, and it will also cause the client to crash, or at least perform that fetching grey screen.