Hello and thank you two,
I experimented _instanceType property by setting its value to _metatype value defined for my stereotype (I hope to be clear...). Drag'n Drop an element from the browser window let me opt an instance of my stereotyped class. But then:
1. I don't catch the difference (aspect and behavior) with creating many times stereotyped elements :
EventType1.Date=date1, EventType2.Date=date2, EventType3.Date=date3... vs
date1:EventType1, date2:EventType1, date3.EventType1...(not sure I'm still clear

)
2. There is no visual difference unlike Standard UML profile that underlines name and sets to blue each instance's background.
What I was first expecting was to drag'n drop my stereotyped element directly from a Toolbox (maybe in a specifically configured diagram's stereotype) to instantly get a recolored instance of it, pre-fixed with
<instance_name> and post-fixed with
:<Element_name>...Thx for reading

Eric