OK, Peter…
Not really sufficiently experienced to test your modified version of pppd, but persevered and managed to successfully follow your comprehensive guidance notes!
I can report that there are no references to IPV6CP in the logs and that my IPFire is running OK with pppd version 2.4.9
[root@ipfire ~]# /usr/sbin/pppd --version
pppd version 2.4.9
[root@ipfire ~]# /etc/rc.d/init.d/network start red
Bringing up the red0 interface…
Bringing up the pppoe interface on red0 … [ OK ]
Starting connection daemon… [ OK ]
RTNETLINK answers: No such file or directory
Adding static routes… [ OK ]
Adding static routes… [ OK ]
Mounting network file systems… [ OK ]
[root@ipfire ~]# ps aux | grep pppd | grep noipv6
root 30766 0.0 0.1 7300 3496 pts/0 S 19:29 0:00 /usr/sbin/pppd plugin rp-pppoe.so red0 usepeerdns defaultroute noipdefault noauth default-asyncmap hide-password nodetach noipv6 noaccomp nodeflate nopcomp novj novjccomp nobsdcomp user bthomehub@btbroadband.com lcp-echo-interval 20 lcp-echo-failure 5 mtu 1492 mru 1492
[root@ipfire ~]#
Am I correct to assume that I can apply the normal update, from my current Core 156 to 158 or 159 when they are released, and avoid 157 for the time being?
Hope this makes sense and helps you?
Kind Rgds
Steve