Hello,
1. I haven't changed default "behavior" of attributes but i made changes to add additional features like adding custom fields (image, radio etc.), replacing default fields, using attributes to do do price calculations etc.
2. I don't suggest to alter default behavior of attributes. Woo core and also 3rd party plugins probably conflict with such case.
If you just need a better administration of Attributes with default behavior then i may suggest something else if you tell me how do you want to manage those.
3. No
4. Monday
Let me know if you have any questions.
Regards,
Turker YILDIRIM