There is an unspoken agreement between Wardens not to get captured alive by the Reds because once you are turned into a Red Court Vampire you lose your loyalty to the White Council (if it is just the fact that you turn in to a soulless monster or if there is some Sire-bond going on and the Red that turns you forces you to switch loyalties isn't specifically explained) and you will betray all the secrets you know.
As for magical abilities, it is also said directly that you retain them, but you get the vampiric/necromantic equivalent of it (Dresden describes the power source of Vampire magic as that similar to necromantic energies, un-life magic, where's mortal magic is based on life energy).
If before you turned you could throw a lightning bolt with mortal magic, now you can throw a lightning bolt with necrotic magic. The effect is the same but on a metaphysical level it is like changing polarities and your magic does no longer count as mortal human magic, which is why the Outsiders showing up is such a big deal because it proves there are non-turned human Wizards supporting the Reds.