Q: A problem with pgfplots and coordinates I'm using Jake's code in his answer to How can I automatically mark local extrema with pgfplots and scatter?. Using the mark max style I can retrieve the value for the y-coordinate of the maximum for a function using \pgfplots@metamax. 
Having this value I can use it, for example, to add nodes using the axis cs coordinate system, as the code below shows; however, I cannot use those nodes as coordinates for a new \addplot (uncommet the commented-out line with \addplot and you'll get an error). 
How can I use those named nodes for an \addplot?
The code:
\documentclass[border=3pt]{standalone}
\usepackage{pgfplots}
\usepgfplotslibrary{fillbetween}
\usetikzlibrary{arrows.meta}

\makeatletter
\pgfplotsset{
    /tikz/max node/.style={
        anchor=south,
    },
    mark max/.style={
        point meta rel=per plot,
        visualization depends on={x \as \xvalue},
        scatter/@pre marker code/.code={%
        \ifx\pgfplotspointmeta\pgfplots@metamax
            \def\markopts{}%
            \coordinate (maximum);
            \node [max node] {
                \pgfmathprintnumber[fixed]{\xvalue},%
                \pgfmathprintnumber[fixed]{\pgfplotspointmeta}
            };
        \else
            \def\markopts{mark=none}
        \fi
            \expandafter\scope\expandafter[\markopts]
        },%
        scatter/@post marker code/.code={%
            \endscope
        },
        scatter
    }
}
\makeatother

\pgfmathdeclarefunction{cubic}{1}{%
  \pgfmathparse{-2*(#1+2)*(#1+2)*(#1-2)+40}%
}

\begin{document}        

\begin{tikzpicture}
\begin{axis}[
  axis lines=middle,
  xtick={-2.5,2.5},
  ytick={\empty},
  domain=-2.5:2.5,
  ymin=-1,
  xmin=-4,
  xmax=3,
  clip=false,
] 
% The curve
\addplot [mark max,draw=red,name path=A] plot {cubic(x)};
\makeatletter
\node (A) at (axis cs:-2.5,\pgfplots@metamax) {A};
\node (B) at (axis cs:2.5,\pgfplots@metamax) {B};
%\addplot[name path=B] coordinates {(A) (B)};% doesn't work
\makeatother
\end{axis}
\end{tikzpicture}

\end{document}

Perhaps I am using the wrong approach here. What I want to do is what follows:
I have the graph of a function A drawn using \addplot; this path is named using name path=A. I need to add another \addplot (that will be named B) defined by two points whose x-coordinates are known but whose y-coordinates are calculated adding positive or negative shifts to the y-coordinate for the maximum of A. Then I will use the fillbetween library to fill the area between A and B. How can this be done?
