Having added a Custom Property in Editor, how do we assign an Update function? When creating a custom property via e.g. bpy.props.FloatProperty(), we can specify a user-defined function to be invoked every time the value of said property changes.

Once the property exists, e.g. added via the Properties Editor, how do we assign or re-assign the update function?

The Properties Editor (Blender 2.74) does not offer that, and, in Python, I don't know how to access the property itself, as opposed to merely its value.
I am looking into it myself atm.

some_value = FloatProperty(default=1.0, update=onupdate)


and then I have a function that handles the update

def onupdate(self, context):


it's important that the function handling has self &amp; context as arguments, and returns none.

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