I will soon have a $950 voucher issued by CO. I would like to use the voucher on the following itinerary:

AUS > EWR, CO
EWR > MAN, UA codeshare on CO metal
MAN > LHR, BD
LHR > IAH > AUS, CO

This prices on ITA to $923. If I have to use the CO flight number for EWR > MAN, the fare rises by $195.

So, my questions are as follows:
(1) May a CO-issued TCV be used to book a UA codeshare on CO metal?
(2) Will having the BD flight in the middle of this itinerary cause a problem given that I'm using a CO-issued TCV?
(3) Is the post in the FAQ about "getting back credit from non-refundable tickets" still current? http://www.flyertalk.com/forum/9674698-post51.html

Thanks very much for your help.