Q2: To what extent are user redefinitions of the asset copyright system permissible and binding?
Linden Responces:
A1: [post=776512]The permissions system was designed to create a record of who created an object or design and what their intention was for its reuse. It works largely because it's associated directly with the object. [/post]
A2: [post=776512]It doesn't seem likely that a notecard would serve the same purpose but again, you'd be best served to consult an expert.[/post]
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I'm no lawer; this is just my opinion and i'm not liable for what you do with it (and i'll file a DMCA takedown if you twist it

The question really is "Is the permissions system adequate to express the licensing agreement?"
If the permissions system is inadequate then redefinition is valid.
But if permissions system is adequate then redefinition not only is invalid but could be construed as false advertising if it contradicts the permissions system.
Since people are providing basic redefinitions, the permissions system is inadequate. Redefinition is valid aslong as it is accessable (if the user can't read the license or has to go out of their way then it could be stipulated that it is a deceptive contract; and not legaly binding). If it's not accessable then the user will assume that the permission on the object are what was intended, and this sort of assumption would likely hold up in court.
If you want people to read the License then it's best to name it "License" or have a script that reads the basics of it to them.