You could try using an intermediary Damage and Apply Behaviour effects, in conjunction with the Unit Takes Damage event. While it's not as straight-forward as you could hope for, it'd be the first thing that springs to mind. The only issue I can think of would be that you probably wouldn't be able to find out who applied the Behavior apart from at initial application (unless you want store the 'casting' unit in a Bank, using the Behaviour [if possible] and the target unit as your keys)
This tutorial explains it in greater detail, but you should be able to 'catch' the application of the behavior, along with who applied it (assuming you set up the Effects properly).
Well that'll work though it's kind of annoying to have to use set effects for every attribute modding effect :thdown: Hope they add something like caster of behavior at least for the attribute change event.
Ghan has said he has fixed this. Monovertex please confirm this fix. This was only a problem with people that had signatures in the upper levels like not the special members but the respected members.