These questions go hand-in-hand. I’ve yet to try to use Ghostflame on a Lich but from what I can tell it would be lackluster compared to using it with Warlock.
While the original Soul Feast wasn’t really used that much it would still be nice to have it obtainable for Lich. So to answer the second question I think that yes, Ghostflame Soul Feast should be switched.
The only drawback I see is that Warlock would get it later but from trying to use it when I got it for the first time it’s really not that great out of the box with no skill points and low passive points whereas Soul Feast is fine even without those.
So really I see no reason to just switch Ghostflame to 30 Warlock passive points and Soul Feast to 15.