Using pkgng, but building some ports with custom options

[John Rogers]

Hello.

I'm looking into switching to using pkgng once FreeBSD 10 is released.
I must say that I'm very impressed so far after playing around with
it, but I have run into a question that I have been unable to find the
answer to. Is it possible to use pkg install from pkg.FreeBSD.org for
most packages, use portmaster locally for some packages when I want to
use custom build options and have it all work well together?

A typical scenario that I want to avoid is that I have a custom built
installation of port A. Then one day the package is updated to a new
version on pkg.FreeBSD.org, which overwrites my local install when I
run pkg upgrade.

I have searched for this and found lots of information but no clear answer.

John