Another Factions/Nightfall Question

I already have the prophecy game and i got bored with that but now im interested in getting back.
Am I able to re-chose a secondary profession for either factions/nightfall for my original prophecy char??
or
do i have to start all over again if i wanted to choose another profession?

Also which one would seem better to get?

Once you own Factions you can take your Prophecies char through 2 missions on the new continent to get to the Profession Changer then pay 500g for each secondary you want to unlock. I suspect there will be something similar for Nightfall but you can only unlock the secondaries for each campaign from within that campaign. (ie rit and sin in Factions and paragon and dervish in Nightfall)

As far as which one to get, Nightfall isn't out until the 27th so if you are looking for something immediately then Factions is your choice. Nightfall *appears* to be better than Factions, but that could be very subjective to what one likes, plus we've only had a taste of NF so far.

Factions is good, it offers more content, professions, skills, greens, armor choices, etc plus things like the Alliance Battles.

Ultimately it is your choice.