Overriding dovecot.conf from Userdb Extras

[E.B.]

Hi,

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?

Thanks!