Running Magic Lantern In Custom Mode?

[Brillopad]

I'm new to the world of ML and have researched it thoroughly before deciding to proceed (as I can't afford to brick my camera, however remote a possibility that might be).  However, I'm confused by the following passage in the ML FAQ:

"Probably the safest way to run Magic Lantern (or any third party camera control software) is to use custom modes - in these modes, Canon code does not save user settings to NVRAM."

What are these custom modes and how can I run ML under them?  I've Googled hard for answers, but not found any (apologies if this is touched on elsewhere).

Two other questions for which I've not found answers:

- Are the ML features all set to "off" by default?  I shoot stills rather than video, so there's a whole set of features I won't really need (at least initially), so it would be good if I could just selectively activate those that are relevant.

- One of my lenses (a Sigma 30mm prime) has a front-focusing issue >> will this affect the focus peaking feature?

[g3gg0]

thats the C mode of your camera (top wheel)

[Brillopad]

Many thanks for the fast response >> I'm using a 550D and there isn't a "C" mode on the camera wheel, only a CA.