Sorry, I tried again, and it kind of solves my problem when I specify EditAnywhere for the sub mesh property, as all of its parameter will be accessible through the MyComponent details panel.
This is not really the behaviour I was aiming for, as I do not want the reference to the mesh to be changed.
VisibleAnywhere should allow me to change all the properties of the sub component without being able to change the reference, which is exactly what I want, so should this be considered as a bug ?
As a note, the sub component property can be protected (which is kind of illogical I agree)
Also I found there is the Instanced meta tag that specifies the property is a component reference, but it doesn’t seem to have any effect on my issue