I don't see any where to change these settings. Is this possible? Even manually?
Edit 2 - it looks like isc dhclient does have support.
DHCPv6 functions and options
Prefix delegation (PD) [since 4.1.1]
25 OPTION_IA_PD dhcp6.ia-pd N/A, set by a client and server to create a prefix delegation binding
26 OPTION_IAPREFIX dhcp6.ia-prefix N/A – sent by the client to convey its Identity Association prefix
option dhcp6.ia-pd string;
The ia-pd option is manufactured by clients and servers to create a
Prefix Delegation binding - to delegate an IPv6 prefix to the client.
It is not directly edited in dhcpd.conf(5) or dhclient.conf(5), but
rather is manufactured and consumed by the software.
option dhcp6.ia-prefix string;
The ia-prefix option is placed inside ia-pd options in order to iden-
tify the prefix(es) allocated to the client. It is not directly
edited in dhcpd.conf(5) or dhclient.conf(5), but rather is manufac-
tured and consumed by the software.
The internal DHCP6 server supports the options as well as attached. so the client should be able to do so.
