1. a) RDF MS change: I think it is considered ninja. You can always ask and if they (all) agree on your MS change, take a screenshot of them agreeing and roll for your new MS.
I've heard something of sorts: what you join in as is your MS in RDF.
b) Raid MS change: Whatever MS changes are in raids, are up to RL/ML.
2. Xmog is Greed roll, as I said in this thread before: "Greed = Everything else. Vendor, AH, OS, Xmog."
3. It would be too hard to know who has what PvP spec. Since all PvE raids are done with PvE gear, PvP gets treated as a secondary.