VLAN tagging the WAN port on XG 450

I have the following problem. Our ISP gives us vlan 333. The WAN port is Port10. Found on the web that people first enable the port using dhcp, then add a VLAN interface on that port, so I did that. The web UI showed something like

Port10: 128.0.0.1

Port10.333: 12.17.12.17 gw 12.17.12.16

But it bothered me knowing that there are probably dhcp requests sent out by Port10. So I changed Port10 to a fake IP, 12.17.12.18 with gw 12.17.12.17:

Port10: 12.17.12.19 gw 12.17.12.17

Port10.333: 12.17.12.17 gw 12.17.12.16

Now I see about ten unanswered ARP requests every 15 seconds or so 12.17.12.8 who-has 12.17.12.17. This is also not ideal. I'd like Port10 to be up without an IP, to have VLAN 333 on it, with our touch down IP that we got from the ISP 12.17.12.17. 

I tried to fix this by setting Port10 to None instead of WAN, and guess what, after 

ip addr flush dev Port10 

I indeed got what I wanted:

XG450_WP02_SFOS 17.0.6 MR-6# ip addr | grep Port10

6: Port10: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc mq group 0x02 nfmark 0x8001 nfmark6 0 nettype 0x02 np 0x04 np6 0 state UP group default qlen 1000

22: Port10.333@Port10: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc noqueue group 0x02 nfmark 0 nfmark6 0 nettype 0x02 np 0 np6 0 state UP group default 

    inet 12.17.12.17/30 brd 12.17.12.18 scope global Port10.333

The fly in the soup is, the web UI still shows an IP assigned to Port10. And, if the devices reboots Port10 comes up with the static IP that I set previously.

Question: what to do to have Port10 with no IP and a VLAN id interface on it, with the IP from the ISP?

I could live with a way to perhaps "ip addr del IP dev Port10" but I don't know where to stick this in the startup files of the XG. I can't recognize the underlying system in /etc

Any help would be appreciated,

Thanks!