There are no descriptors in the example you gave. You are writing example code of how you WANT it to work, or wished it would work.
Please write a descriptor that ACTUALLY overrides = (using __set__) and does what you want it to do, and then use it in an actual example. It may not look the way you like, but it certainly can be done. Only then can we have a meeting of minds, I think.
As things stand right now, it seems like you don't understand what we are saying about using descriptors to accomplish this. However it is certainly possible I simultaneously don't understand what you are really trying to do in the code you wrote (I definitely don't claim to).