Macro.
/assist Name
Just edit the name as the group changes.
That functionality is not currently in game. %t is your offensive target and %dt is your defensive target. The /assist command works for defensive target but not for offensive target. VR may or may not implement that functionality. To my knowledge they have not addressed this specific request.
The Pantheon Discord is where most discussion about the game happens, and where most interactions between Devs and players takes place. Any suggestion is more likely to be seen by the Devs there than most any place else. The "General Feedback" channel in the Testers section would probably be the best place to post about it.
I have heard this functionality talked about occasionally in various places, though never heard a Dev talking about it.