Yes. Every user should be able to delete cookies. It would be really miserable if they were prevented from doing so. Your application just needs to handle and communicate the situation to the user the right way.
uuid.getnode()
What makes you think that this function is able to retrieve information about a remote computer? How would you even choose which machine to get the information from? The function gets the MAC address from the machine the code runs on.
Note that MAC address is not guaranteed to be constant. 1. The interface can be replaced. 2. The MAC can be changed. 3. The network interface can be virtual with a dynamically generated MAC. 4. A machine can have an IP connectivity without having a MAC address.
Is your application limited to the local network without routers in the way? I.e. the clients are in the same broadcast domain on a network switch as the server?
If so then there are ways how to get the MAC address (with some limitations).
Otherwise there is no standardized way and you would need to use a software running on the client - the agent I mentioned.
I noticed that you opened a new topic about this: