Hi Daniel, and sorry for the late answer.
I had no time to build you some example in hype, but I will as soon as I can.
For this request, I was dreaming about that ability to assign data attributes to symbols with the same ui as custom behaviours, so a textfield for naming the data attribute and then a second one to assign a value to it. The reason why, here's an example :
In conclusion, I could have only one "clock symbol" in the library and instantiate it with some different values (ex data-hour=2, data-minute=6)
Do you understand what I mean ? (sorry English is not my mother tongue)