Cannot change curve modifier after pressing 'Apply' Sorry for my trivial question.
I'm a newbie and I'm walking through a cave tutorial. I can deform a mesh with a NURBS curve but I can't further edit the deformation through manipulating the curve after applying the modifier. Pressing Apply on the modifier 'freezes' the effect and the modifier icon in the object tree disappears (is that a standard behaviour?). Moreover, when the mouse pointer is over the Apply or Apply as Shape buttons, I read the same tip: 'Apply modifier and remove from the stack'. Is that a bug? My configuration is Blender 2.72b on Ubuntu 12.04 LTS (64 bit).

EDIT: I can edit the deformation before the modifier is applied. I expected a further deformation editing through the curve manipulating because I am too influenced by CATIA :)
The purpose of 'Applying' a modifier is to make the changes that the modifier has made, permanent. Any deformation or change to the geometry a modifier may have caused will overwrite the original geometry.

As long as the modifiers are present in the modifier 'stack' (where the modifiers get listed), they will be able to be edited.

I have not followed every step of the tutorial you linked to, but unless the tutorial says to apply the modifier there is no need to. It is perfectly fine to have many modifiers on an object and never apply them, allowing non-destructive editing.

See more information about modifiers and the modifier stack in the Blender Manual.