The token command explicitly configures the lower 64 bits that will be used with any autoconf
address, as opposed to one derived from the macaddr. This aligns the autoconf-assigned address with
the fixed one set above, and can do so as a pre-up command to avoid ever having another address
even temporarily, when this is all set up before boot.

https://man7.org/linux/man-pages/man8/ip-token.8.html

sudo sysctl -w net.ipv6.conf.all.forwarding=0
sudo ip token set ::192:0:2:1 dev eth1
sudo sysctl -w net.ipv6.conf.all.forwarding=1

List tokens:

vyos@r14# sudo ip token list
token :: dev eth0
token ::192:0:2:1 dev eth1
[edit]
vyos@r14#

Expecting DHCPv6 address with configured host address, something like:

set interfaces ethernet eth1 address dhcpv6 

2001:db8:23:192:0:2:1/64

So it doesn't depend on which network we get, host part perhaps will be the same eve if we change the NIC

Proposed syntax (depends on prefix):

set interfaces ethernet eth1 ipv6 token ::192:0:2:1/64
or 
set interfaces ethernet eth1 ipv6 token ::11