(As always, thank you for reading. The below is personal opinion only and does not represent the opinions of others)
SUGGESTION: When a formula is completed with |to|, |from|, or |at| text modifier, it should directly effect that stat:
i.e.
/roll 1d10*2 |to| (HP)
The above would add the result to the HP stat for the player, taking them from say 120, to a theoretical 140 (if it was a perfect roll.) Likewise, if the player reverses it:
/roll 1d10*2 |from| (HP)
This formula would remove the resulting number from the target stat.
I think this could be amplified if you added a modifier as well.
/roll 1d10*2 |from| |target| (HP)
This would prompts the user, when the macro was run, to choose a target. The target would be selectable from the available on screen units with the available stat. (i.e. If a character doesn't HAVE HP as a stat, then they wouldn't be presented for selection by the popup.
Just a point of clarification, that |at| would be used in an instance where the result of a roll/formula could be a negative or positive integer. This way, |at| dictates that the result will be added or subtracted based entirely on what the final number is.