Overriding dovecot.conf from Userdb Extras

[E.B.]

> I thought I read that anything from dovecot.conf can be
> overridden in a
> userdb lookup. Or a passdb lookup with "userdb_" prefix.
>
> But I tried for fun change log_path but it never worked. Is
> that because
> logging is special, already started logging before it comes
> to the
> passdb/userdb lookups?  So are there some dovecot.conf
> settings
> that cannot be overridden?

Any takers?