Can I switch side between Kurzick and Luxon later?

I am wondering if I could switch side since I want to do all possibile quests.

Can I switch side after I have choosen a side, also, when would I need to choose?

I do believe you can switch sides at any point - all it involves is getting faction points in the faction you want to switch to. IE say your in Kurzick and want to be in Luxiom .. go and do Luxom quest's to get luxom faction and cash that it to switch Allegiance from Kurzick to Luxom..

At least thats how I believe it's supposed to be - I believe your supposed to be able to do both sides with 1 character if you want.