I did know of the effect, and one can change stats on both sides of the bar.
I have stumbled on something similar in the past that removes the "green life bar" completely. The unit remains as a target and retains the negative damage amount for HP life.
Trigger 0:
no
on
no
Condition 0:
whatever
Effect 0:
Change Object HP (-)negative units amount
Effect 1:
Damage Object (-)negative units amount
This is good for creating those low HP units that are in some RPS scenarios. This way there is no more red bars over lower HP units. It also completey removes the bar from the field shown above.
"I take it that this is the Anastasia Scud pines for?" - Epic Commander
"What Ana said. Use sugar and the whip." - aka the Pilot
"I think you will realize the emphasis was on Ana and Cake." - Monk