Your event #10 is one condition. It will never work because the GravityTimeMultiplier variable can't be 1, and 2, and 3 etc. at the same time.
Each condition should be in a separate event:
GravityTimeMultiplier=1 Set gravity to 2
GravityTimeMultiplier=2 Set gravity to 5
And so on.
If you want all new balloons to be created with the same physics properties, you need to set them in editor on that balloon sprite that you have outside of the layout. It's a "default" instance for balloon object, and all new instances, when created, will be copied from it.
You don't see any difference in density and elasticity because they are only visible when physic objects interact with each other or with immovable objects.