Normally, IPv6 addresses are assigned via SLAAC, where the router provides the network prefix and the client device creates the suffix, using either the MAC address or a random number. Those addresses will not change unless the prefix does. You can filter on those addresses for incoming traffic. However, you usually can't filter on the address for outgoing traffic, as something called privacy addresses are used, which will change daily.
https://en.wikipedia.org/wiki/IPv6#Stateless_address_autoconfiguration_.28SLAAC.29