Thank you for the response.

So I will need to use 2 separate slots? One for Regen under normal healing situations, and another for Regen on the tank when DPSing?

Would you be able to give any examples?
I'm not a big macro user and my head is spinning trying to figure this out. ^^;

I'm trying:
/assist <t>
/ac "Regen" <t>

While focused on a boss, I think this would cast Regen on the main tank?
But if I am focused on the tank, it would try to Regen the boss... which would then end up casting on me instead?

Oh, I use a controller on a PC and I think I don't have R3 or L3 buttons.