Save multiple object variable at once?

The question is in the title…
I have multiple instances of one object in my scene. All this objects are part of the same group object and they all have an object variable called “presence” equal to 0 or 1.
Is it possible to save all the value with one event? :question:

Use “for each” event.

For each object “MyGroup” :
do = “something” to the variable “presence” of “Mygroup”

God bless you!
The french translation for that event isn’t very clear…