With a command...
R1(config-if)#ipv6 address 2001:5c0:1400:a::331/64 eui-64
...one can configure an address for an interface with EUI-64 part generated from actual MAC address on this interface.
How to make router to generate EUI-64 with random numbers, without revealing actual MAC address and if possible last 64 bits of IPv6-address are randomly changed from time to time ?