Changing layer levels via expressions

I’ve created my basic game, with map and pieces using layers and levels to track different traits (firepower, strength, that sort of thing). I’m using levels but am open to using dynamic properties if that’s the way to go.

My problem is understanding how to actually use expressions and the handful of “action” tools such a trigger, global keys or whatever to do something that seems, at first, simple. I don’t know if I’m simply trying to do something VASSAL really isn’t designed for or if I’m just unable to sort it out.

Here’s what I want to do: Send, invoke or otherwise trigger a FIRE event that the gamepiece can recognize and evaluate. Based on the numerical value of the FIRE event, I would like the piece to change values for various levels. If I can just get a simple Event - change stuff procedure figured out, I can go from there. I know that global keys can send an event to ALL pieces. I just want one for the selected piece.

Am I trying to do something that really isn’t in the toolbox or is it fight in front of me and I’m just not seeing it.