I just imported some footage shot on a Canon 550d T2i on NTSC. ( I used the Log and Transfer).
After transfering the footage I noticed that the Audio/Video Setting was still on PAL.
Now, is it enough to change the setting now or is it necessary to start a new project and re-transfer all the footage after switching the Ntsc setting?
Late answer, you probably figured it out. There's no need to re-import the footage. The footage has its own characteristic Pal or NTSC. Your timeline has different settings though, so it's important to start with a timeline with the right setting.