Rigid Body and property modification

is there a way to modify an object property during a rigidbody simultaition?
For example if an object enters in (or exit) a specific area during the simulation I need to change some object property like position/size/rotation.
I was looking to an automatic solution, so avoiding keyframes.
It looks I an not able to specify these actions with constrains, so I am thinking that maybe only scripts can help (if possible).