I believe the OP is asking basically this:
They hover over a player in the group window with the cursor.
Now, lets say 1 is their hotkey for "Cure Minor Wounds". What I think the OP would like is for them to be able to hit 1 and for that spell to be cast on the player their cursor is over, rather than their current target.
If that is correct, then to my knowledge this that is not possible -- the game simply doesn't work that way.
If you are talking about the group window, then it might be possible to gin up a pseudo-hotbar and combine that with a modded player window so that it does /useabilityonplayer <whatever> and detects the player via the hovering part... but to my knowledge no UI does this and it would have to be done via a special hotbar that would not function like a normal hotbar.
So the short answer is "No," and the long answer is "Might be possible" but with the caveat of it likely being a kludge and the fact you would have to script your own kind of hotbar.
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