The only times you actually need to change from your lead to another toon are:
a) The lead is under a CC effect, which occasionally prevents your slaves from registering target changes... but swapping to a new lead, or even to anything and back to the previous will remove this restriction.
b) The lead has been killed, and either looted or the battle has moved beyond what he can see.

Just about any software will let you switch to a different toon, who is on the same computer.
With some the swap is instant, with others it might take a few seconds.
But you should be good to go, thereafter.

Even if you're not using an FTL assist.
Whether your assist is Focus based, Target based or Leader based, the act of switching to the new window will also send the leader update to the team.
Meaning, with even very minimal macros, the team can continue without issue.